diff --git a/telemetry/definitions/commonDefinitions.json b/telemetry/definitions/commonDefinitions.json
index 5b074f308..1fb913234 100644
--- a/telemetry/definitions/commonDefinitions.json
+++ b/telemetry/definitions/commonDefinitions.json
@@ -1782,7 +1782,7 @@
         {
             "name": "source",
             "type": "string",
-            "description": "The source of the operation"
+            "description": "The source of the operation. This answers 'who' caused/triggered the operation. Example: did an Auth signout happen because of some expiration or since the user explicitly clicked the signout button."
         },
         {
             "name": "sourceFacetType",
diff --git a/telemetry/vscode/src/generate.ts b/telemetry/vscode/src/generate.ts
index 3a3b2abd7..f811291f2 100644
--- a/telemetry/vscode/src/generate.ts
+++ b/telemetry/vscode/src/generate.ts
@@ -136,6 +136,7 @@ const commonMetadata = [
     'requestId',
     'requestServiceType',
     'result',
+    'source',
 ] as const
 
 /**
diff --git a/telemetry/vscode/test/resources/generatorOutput.ts b/telemetry/vscode/test/resources/generatorOutput.ts
index 5ed19bd36..289ce0024 100644
--- a/telemetry/vscode/test/resources/generatorOutput.ts
+++ b/telemetry/vscode/test/resources/generatorOutput.ts
@@ -30,6 +30,8 @@ export interface MetricBase {
     readonly requestServiceType?: string
     /** The result of the operation */
     readonly result?: Result
+    /** The source of the operation. This answers 'who' caused/triggered the operation. Example: did an Auth signout happen because of some expiration or since the user explicitly clicked the signout button. */
+    readonly source?: string
     /** A flag indicating that the metric was not caused by the user. */
     readonly passive?: boolean
     /** @deprecated Arbitrary "value" of the metric. */
diff --git a/telemetry/vscode/test/resources/generatorOverrideOutput.ts b/telemetry/vscode/test/resources/generatorOverrideOutput.ts
index 18a297141..ad39b3362 100644
--- a/telemetry/vscode/test/resources/generatorOverrideOutput.ts
+++ b/telemetry/vscode/test/resources/generatorOverrideOutput.ts
@@ -30,6 +30,8 @@ export interface MetricBase {
     readonly requestServiceType?: string
     /** The result of the operation */
     readonly result?: Result
+    /** The source of the operation. This answers 'who' caused/triggered the operation. Example: did an Auth signout happen because of some expiration or since the user explicitly clicked the signout button. */
+    readonly source?: string
     /** A flag indicating that the metric was not caused by the user. */
     readonly passive?: boolean
     /** @deprecated Arbitrary "value" of the metric. */