--- 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