Wolfram Research, Inc.
You can ask Mathematica to abort at any point in a computation, either by calling the function Abort[ ], or by typing appropriate interrupt keys.
When asked to abort, Mathematica will terminate the computation as quickly as possible. If the answer obtained would be incorrect or incomplete, then Mathematica returns $Aborted instead of giving that answer.
Aborts can be caught using CheckAbort, and can be postponed using AbortProtect.