The Expanded widget in Flutter is used within a Row, Column, or Flex widget to give a child widget the flexibility to expand and occupy the available space along the main axis (horizontal in a Row and vertical in a Column). It allows the child widget to take up as much space as possible within its parent.

                 
              import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Expanded Example'),
        ),
        body: Column(
          children: <Widget>[
            Container(
              color: Colors.blue,
              height: 100,
              width: double.infinity, // Container takes full width of the screen
              child: Center(
                child: Text(
                  'Top Container',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
            Expanded(
              // Expanded widget fills available space
              child: Container(
                color: Colors.green,
                child: Center(
                  child: Text(
                    'Expanded Container',
                    style: TextStyle(color: Colors.white),
                  ),
                ),
              ),
            ),
            Container(
              color: Colors.blue,
              height: 100,
              width: double.infinity, // Container takes full width of the screen
              child: Center(
                child: Text(
                  'Bottom Container',
                  style: TextStyle(color: Colors.white),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}