Add natively instrumented to glossary (#4186)

CHANGELOG.md

@@ -42,6 +42,8 @@ release.
 
 - Update instrumentation library guidance to avoid naming collisions between external and OTel instrumentations.
   ([#4187](https://github.com/open-telemetry/opentelemetry-specification/pull/4187))
+- Add natively instrumented to glossary.
+  ([#4186](https://github.com/open-telemetry/opentelemetry-specification/pull/4186))
 
 ### Supplementary Guidelines
 

specification/glossary.md

@@ -21,6 +21,7 @@ Some other fundamental terms are documented in the [overview document](overview.
   * [In-band and Out-of-band Data](#in-band-and-out-of-band-data)
   * [Manual Instrumentation](#manual-instrumentation)
   * [Automatic Instrumentation](#automatic-instrumentation)
+  * [Natively Instrumented](#natively-instrumented)
   * [Telemetry SDK](#telemetry-sdk)
   * [Constructors](#constructors)
   * [SDK Plugins](#sdk-plugins)
@@ -112,6 +113,16 @@ monkey patching, or running eBPF programs.
 
 Synonym: *Auto-instrumentation*.
 
+### Natively Instrumented
+
+Denotes a library or application that uses the OpenTelemetry API directly to provide built-in instrumentation, thus
+*instrumented library* and *instrumentation library* are the same library.
+
+If a separate *instrumentation library* or a plugin is required to instrument a library or application,
+that *instrumented library* or application must not be called *natively instrumented*, even if the
+*instrumentation library* or plugin is provided by the same authors or is a plugin that fits into
+the ecosystem of the given software.
+
 ### Telemetry SDK
 
 Denotes the library that implements the *OpenTelemetry API*.