A Layer 2 (L2) network processes transactions separately from its underlying base blockchain (Layer 1), then periodically settles a summary back to that base layer — inheriting much of its security while offering faster, cheaper transactions. Rollups are the most common Layer 2 design in use today.
Moving funds between a Layer 1 network and a Layer 2 (or between two Layer 2s) generally requires a bridge, which is a higher-stakes step than an ordinary transaction and worth treating with extra caution.