Plain English Meaning
When you fly from one controller's area into another's, the first controller passes you to the next one. They confirm who you are on radar and tell you which frequency to switch to so you keep talking to the right person.
Full Definition
An action taken to transfer the radar identification of an aircraft from one controller to another controller if the aircraft will enter the receiving controller's airspace and radio communications with the aircraft will be transferred.
Context Anchor
Pilots encounter handoffs during ATC communications, especially on cross-country flights, instrument flights, and when moving between , , , , or tower .