docs: add Engine glossary entry

src/content/resources/architectural-overview.md

@@ -92,20 +92,16 @@ the primitives necessary to support all Flutter applications.
 The engine is responsible for rasterizing composited scenes
 whenever a new frame needs to be painted.
 It provides the low-level implementation of Flutter's core API,
-including graphics (through [Impeller][]
-on iOS, Android, and desktop (behind a flag),
-and [Skia][] on other platforms), text layout,
-file and network I/O, accessibility support,
-plugin architecture, and a Dart runtime
+including graphics text layout, file and network I/O, a Dart runtime,
 and compile toolchain.
 
 :::note
 If you have a question about which devices support
-Impeller, check out [Can I use Impeller?][]
+Impeller, check out [Impeller availability][]
 for detailed information.
 :::
 
-[Can I use Impeller?]: {{site.main-url}}/go/can-i-use-impeller
+[Impeller availability]: {{site.main-url}}/go/can-i-use-impeller
 [Skia]: https://skia.org
 [Impeller]: /perf/impeller
 
@@ -588,7 +584,7 @@ such as Windows or macOS.
 
 :::note
 If you want to know which devices Impeller supports,
-check out [Can I use Impeller?][].
+check out [Impeller availability][].
 For more information,
 visit [Impeller rendering engine][]
 :::

src/data/glossary.yml

@@ -1,3 +1,33 @@
+- term: "Engine"
+  short_description: |-
+    The portable runtime for Flutter apps.
+  long_description: |-
+    The engine is Flutter's platform-agnostic logic that's written
+    in native code, mostly C++.
+
+    The main responsibilities of the engine are as follows:
+
+    1. Exposes the `dart:ui` API, which are the low-level primitives
+       that the Flutter framework builds upon.
+    2. Converts low-level drawing commands into pixels (also called
+       _rasterization_, this includes Impeller and Skia).
+    3. Responsible for launching and managing Dart's runtime.
+    4. Responsible for laying out text.
+    5. Responsible for asset resolution.
+
+    [framework]: /resources/architectural-overview#architectural-layers
+    [Impeller]: /resources/glossary#impeller
+  related_links:
+    - text: "Architectural overview: The Engine"
+      link: "/resources/architectural-overview#architectural-layers"
+      type: "doc"
+    - text: "Engine repository"
+      link: "https://github.com/flutter/flutter/tree/main/engine/src/flutter"
+      type: "code"
+  labels:
+    - "engine"
+    - "architecture"
+
 - term: "Hot reload"
   short_description: |-
     A Flutter feature that allows you to inject updated code into