---
title: Glossary
description: >-
  Terminology you may or may not be familiar with used by the OpenTelemetry
  project.
weight: 200
---

The OpenTelemetry project uses terminology you might not be familiar with. In
addition, the project defines the terminology in a different way than others.
This page captures terminology used in the project and what it means.

## Generic terminology

### **Aggregation**

The process of combining multiple measurements into exact or estimated
statistics about the measurements that took place during an interval of time,
during program execution. Used by the [Metric](#metric)
[Data source](#data-source).

### **API**

Application Programming Interface. In the OpenTelemetry project, used to define
how telemetry data is generated per [Data source](#data-source).

### **Application**

One or more [Services](#service) designed for end users or other applications.

### **APM**

Application Performance Monitoring is about monitoring software applications,
their performance (speed, reliability, availability, and so on) to detect
issues, alerting and tooling for finding the root cause.

### **Attribute**

OpenTelemetry term for [Metadata](#metadata). Adds key-value information to the
entity producing telemetry. Used across [Signals](#signal) and
[Resources](#resource). See [attribute spec][attribute].

### **Automatic instrumentation**

Refers to telemetry collection methods that do not require the end-user to
modify application's source code. Methods vary by programming language, and
examples include bytecode injection or monkey patching.

### **Baggage**

A mechanism for propagating [Metadata](#metadata) to help establish a causal
relationship between events and services. See [baggage spec][baggage].

### **Client library**

See [Instrumented library](#instrumented-library).

### **Client-side app**

A component of an [Application](#application) that is not running inside a
private infrastructure and is typically used directly by end-users. Examples of
client-side apps are browser apps, mobile apps, and apps running on IoT devices.

### **Collector**

A vendor-agnostic implementation on how to receive, process, and export
telemetry data. A single binary that can be deployed as an agent or gateway.

Also known as the OpenTelemetry Collector. More on the Collector
[here][collector].

### **Contrib**

Several [Instrumentation Libraries](#instrumentation-library) and the
[Collector](#collector) offer a set of core capabilities as well as a dedicated
contrib repository for non-core capabilities including vendor `Exporters`.

### **Context propagation**

Allows all [Data sources](#data-source) to share an underlying context mechanism
for storing state and accessing data across the lifespan of a
[Transaction](#transaction). See [context propagation
spec][context propagation].

### **DAG**

[Directed Acyclic Graph][dag].

### **Data source**

See [Signal](#signal)

### **Dimension**

A term used specifically by [Metrics](#metric). See [Attribute](#attribute).

### **Distributed tracing**

Tracks the progression of a single [Request](#request), called a
[Trace](#trace), as it is handled by [Services](#service) that make up an
[Application](#application). A [Distributed trace](#distributed-tracing)
transverses process, network and security boundaries.

See [Distributed tracing][distributed tracing].

### **Distribution**

A distribution is a wrapper around an upstream OpenTelemetry repository with
some customizations. See [more][distribution].

### **Event**

Something that happened where representation depends on the
[Data source](#data-source). For example, [Spans](#span).

### **Exporter**

Provides functionality to emit telemetry to consumers. Exporters can be push- or
pull-based.

### **Field**

A term used specifically by [Log Records](#log-record). [Metadata](#metadata)
can be added through defined fields, including [Attributes](#attribute) and
[Resource](#resource). Other fields may also be considered `Metadata`, including
severity and trace information. See the [field spec][field].

### **gRPC**

A high-performance, open source universal [RPC](#rpc) framework. More on gRPC
[here](https://grpc.io).

### **HTTP**

Short for [Hypertext Transfer Protocol][http].

### **Instrumented library**

Denotes the [Library](#library) for which the telemetry signals
([Traces](#trace), [Metrics](#metric), [Logs](#log)) are gathered. See
[more][spec-instrumented-lib].

### **Instrumentation library**

Denotes the [Library](#library) that provides the instrumentation for a given
[Instrumented library](#instrumented-library).
[Instrumented library](#instrumented-library) and
[Instrumentation library](#instrumentation-library) can be the same
[Library](#library) if it has built-in OpenTelemetry instrumentation. See [the
lib specification][spec-instrumentation-lib].

### **JSON**

Short for [JavaScript Object Notation][json].

### **Label**

A term used specifically by [Metrics](#metric). See [Metadata](#metadata).

### **Language**

Programming Language.

### **Library**

A language-specific collection of behavior invoked by an interface.

### **Log**

Sometimes used to refer to a collection of [Log records](#log-record). Can be
ambiguous since people also sometimes use [Log](#log) to refer to a single
[Log record](#log-record). Where ambiguity is possible, use additional
qualifiers, for example, `Log record`. See [more][log]

### **Log record**

A recording of an [Event](#event). Typically. the record includes a timestamp
indicating when the [Event](#event) happened as well as other data that
describes what happened, where it happened, and so on. See [more][log record].

### **Metadata**

A key-value pair, for example `foo="bar"`, added to an entity producing
telemetry. OpenTelemetry calls these pairs [Attributes](#attribute). In
addition, [Metrics](#metric) have [Dimensions](#dimension) an [Labels](#label),
while [Logs](#log) have [Fields](#field).

### **Metric**

Records a data point, either raw measurements or predefined aggregation, as time
series with [Metadata](#metadata). See [more][metric].

### **OC**

Short form for [OpenCensus](#opencensus).

### **OpenCensus**

A set of libraries for various languages that allow you to collect application
metrics and distributed traces, then transfer the data to a backend of your
choice in real time.
[Precursor to OpenTelemetry](/docs/what-is-opentelemetry/#history). See
[more][opencensus].

### **OpenTracing**

Vendor-neutral APIs and instrumentation for distributed tracing.
[Precursor to OpenTelemetry](/docs/what-is-opentelemetry/#history). See
[more][opentracing].

### **OT**

Short form for [OpenTracing](#opentracing).

### **OTel**

Short form for [OpenTelemetry](/docs/what-is-opentelemetry/).

### **OTelCol**

Short form for [OpenTelemetry Collector](#collector).

### **OTLP**

Short for [OpenTelemetry Protocol](/docs/specs/otlp/).

### **Propagators**

Used to serialize and deserialize specific parts of telemetry data such as span
context and [Baggage](#baggage) in [Spans](#span). See [more][propagators].

### **Proto**

Language independent interface types. See [more][proto].

### **Receiver**

The term used by the [Collector](/docs/collector/configuration/#receivers) to
define how telemetry data is received. Receivers can be push- or pull-based. See
[more][receiver].

### **Request**

See [Distributed Tracing](#distributed-tracing).

### **Resource**

Captures information about the entity producing telemetry as
[Attributes](#attribute). For example, a process producing telemetry that is
running in a container on Kubernetes has a process name, a pod name, a
namespace, and possibly a deployment name. All these attributes can be included
in the `Resource`.

### **REST**

Short for [Representational State Transfer][rest].

### **RPC**

Short for [Remote Procedure Call][rpc].

### **Sampling**

A mechanism to control the amount of data exported. Most commonly used with the
[Tracing](#trace) [Data Source](#data-source). See [more][sampling].

### **SDK**

Short for Software Development Kit. Refers to a telemetry SDK that denotes a
[Library](#library) that implement the OpenTelemetry [API](#api).

### **Semantic conventions**

Defines standard names and values of [Metadata](#metadata) in order to provide
vendor-agnostic telemetry data.

### **Service**

A component of an [Application](#application). Multiple instances of a
[Service](#service) are typically deployed for high availability and
scalability. A [Service](#service) can be deployed in multiple locations.

### **Signal**

One of [Traces](#trace), [Metrics](#metric) or [Logs](#log). More on Signals
[here][signals].

### **Span**

Represents a single operation within a [Trace](#trace). See [more][span].

### **Span link**

A span link is a link between causally-related spans. For details see
[Links between spans](/docs/specs/otel/overview#links-between-spans) and
[Specifying Links](/docs/specs/otel/trace/api#specifying-links).

### **Specification**

Describes the cross-language requirements and expectations for all
implementations. See [more][specification].

### **Status**

The result of the operation. Typically used to indicate whether an error
occurred. See [more][status].

### **Tag**

See [Metadata](#metadata).

### **Trace**

A [DAG](#dag) of [Spans](#span), where the edges between [Spans](#span) are
defined as parent-child relationship. See [more][trace].

### **Tracer**

Responsible for creating [Spans](#span). See [more][tracer].

### **Transaction**

See [Distributed Tracing](#distributed-tracing).

### **zPages**

An in-process alternative to external exporters. When included, they collect and
aggregate tracing and metrics information in the background; this data is served
on web pages when requested. See [more][zpages].

[baggage]: /docs/specs/otel/baggage/api/
[attribute]: /docs/specs/otel/common/#attributes
[collector]: /docs/collector
[context propagation]: /docs/specs/otel/overview#context-propagation
[dag]: https://en.wikipedia.org/wiki/Directed_acyclic_graph
[distributed tracing]: /docs/concepts/signals/traces/
[distribution]: /docs/concepts/distributions/
[field]: /docs/specs/otel/logs/data-model#field-kinds
[http]: https://en.wikipedia.org/wiki/Hypertext_Transfer_Protocol
[json]: https://en.wikipedia.org/wiki/JSON
[log]: /docs/specs/otel/glossary#log
[log record]: /docs/specs/otel/glossary#log-record
[metric]: /docs/concepts/signals/metrics/
[opencensus]: https://opencensus.io
[opentracing]: https://opentracing.io
[propagators]: /docs/languages/go/instrumentation/#propagators-and-context
[proto]: https://github.com/open-telemetry/opentelemetry-proto
[receiver]: /docs/collector/configuration/#receivers
[rest]: https://en.wikipedia.org/wiki/Representational_state_transfer
[rpc]: https://en.wikipedia.org/wiki/Remote_procedure_call
[sampling]: /docs/specs/otel/trace/sdk#sampling
[signals]: /docs/concepts/signals/
[span]: /docs/specs/otel/trace/api#span
[spec-instrumentation-lib]: /docs/specs/otel/glossary/#instrumentation-library
[spec-instrumented-lib]: /docs/specs/otel/glossary/#instrumented-library
[specification]: /docs/concepts/components/#specification
[status]: /docs/specs/otel/trace/api#set-status
[trace]: /docs/specs/otel/overview#traces
[tracer]: /docs/specs/otel/trace/api#tracer
[zpages]:
  https://github.com/open-telemetry/opentelemetry-specification/blob/main/experimental/trace/zpages.md
