a rectangular groove made to hold two pieces together
source: WordNet 3.0
A longitudinal channel, groove, or recess cut out of the edge or face of any body; especially, one intended to receive another member, so as to break or cover the joint, or more easily to hold the members in place; thus, the groove cut for a panel, for a pane of glass, or for a door, is a rabbet, or rebate.
