A Jump-cancelled grab can be performed by jump-cancelling a run or dash, and pressing Z or L/R and the A button. The character performs the standing grab animation while sliding forward slightly (depending on traction). For most characters, JC'd grabs have less startup and/or cooldown lag than standard dash-grabs.
Jump-Cancelled grabs have slightly larger hitboxes than standard (though still smaller than actual dash-) grabs, and are primarily used in chain-grabs (though not in Peach's chaingrab).
Abbreviated JC'd grab.