In traditional joinery, this is the margin of uncut wood between the edge of a joint and the end of the board. On a mortise, it is the material left at the end of a stile that stops the mortise from becoming an open slot. On a tenon, it is the shoulder width left after cutting away material to fit a blind mortise. Sufficient relish is required to prevent the wood from splitting under structural stress.
Leave at least an inch of relish on the bottom of those door stiles so the mortise doesn't blow out when we assemble it.
Related terms
Mortise-and-tenon joint
A traditional wood joint connecting two pieces at a right angle by inserting a peg into a hole.
Mortise
A cavity or rectangular hole cut into a piece of wood to receive a matching projection.
Blowout
The splintering and tear-out that occurs on the exit side of a cut or drilled hole.