Both put more line outside the rod tip, but they are not the same action.

Shooting line is a release after the stop: the loop takes line and the amount outside the tip increases. Nothing else is asked of the rod. Slipping line also increases the line outside the tip, but it combines the release with rod movement, either before or after a casting stroke.

The stop is the clearest test. If line leaves your hand only after the rod has stopped, that is shooting. If the release is paired with rod movement before or after a casting stroke, that is slipping.

The two definitions share their first clause — “increasing amount of fly line outside rod tip” — so the words alone will not tell you which is which. The separation is in the timing and in what the rod is doing.

On the lawn you can feel it. Release line together with a rod movement before or after a stroke and you have slipped; let it go after the stop and you have shot.

Source

From the FFI Fly Casting Definitions (August 2025); terms follow the FFI Fly Casting Definitions (Shooting Line, Slipping Line).