Flutter: Expanded vs Flexible

I've used both Expanded and Flexible widgets and they both seem to work the same.

What is the difference between Expanded and Flexible?

Scaffold(
  appBar: AppBar(),
  body: Column(
    children: <Widget>[
      Row(
        children: <Widget>[
          buildExpanded(),
          buildFlexible(),
        ],
      ),
      Row(
        children: <Widget>[
          buildExpanded(),
          buildExpanded(),
        ],
      ),
      Row(
        children: <Widget>[
          buildFlexible(),
          buildFlexible(),
        ],
      ),
    ],
  ),
);