Fix Stack references in Overlay docs (#89025)

packages/flutter/lib/src/widgets/overlay.dart

@@ -214,10 +214,10 @@ class _OverlayEntryWidgetState extends State<_OverlayEntryWidget> {
   }
 }
 
-/// A [Stack] of entries that can be managed independently.
+/// A stack of entries that can be managed independently.
 ///
 /// Overlays let independent child widgets "float" visual elements on top of
-/// other widgets by inserting them into the overlay's [Stack]. The overlay lets
+/// other widgets by inserting them into the overlay's stack. The overlay lets
 /// each of these widgets manage their participation in the overlay using
 /// [OverlayEntry] objects.
 ///
@@ -225,12 +225,18 @@ class _OverlayEntryWidgetState extends State<_OverlayEntryWidget> {
 /// overlay created by the [Navigator] in a [WidgetsApp] or a [MaterialApp]. The
 /// navigator uses its overlay to manage the visual appearance of its routes.
 ///
+/// The [Overlay] widget uses a custom stack implementation, which is very
+/// similar to the [Stack] widget. The main use case of [Overlay] is related to
+/// navigation and being able to insert widgets on top of the pages in an app.
+/// To simply display a stack of widgets, consider using [Stack] instead.
+///
 /// See also:
 ///
-///  * [OverlayEntry].
-///  * [OverlayState].
-///  * [WidgetsApp].
-///  * [MaterialApp].
+///  * [OverlayEntry], the class that is used for describing the overlay entries.
+///  * [OverlayState], which is used to insert the entries into the overlay.
+///  * [WidgetsApp], which inserts an [Overlay] widget indirectly via its [Navigator].
+///  * [MaterialApp], which inserts an [Overlay] widget indirectly via its [Navigator].
+///  * [Stack], which allows directly displaying a stack of widgets.
 class Overlay extends StatefulWidget {
   /// Creates an overlay.
   ///