A rabbet is a recess cut across the end or along the edge of a board. Essentially it is a dado that has one side off the end or edge of the board.
Rabbet joints usually only present end grain to long grain surfaces for gluing, and since this is a relatively weak situation, rabbet joints should be supplemented with fasteners.
Rabbet joints are primarily found at the corners of cases, such as between drawer sides and fronts, or top-and-bottom to sides of vertical cases.
When referring to rabbet joints at the end of a board, the depth is the distance measured from the face of the board, and the width is the distance measured from the end of the board. The cheek is the face formed on the tenon produced by the rabbet, and the shoulder is the face with end grain inside the portion that was rabbeted.
This is the most basic form of rabbet joint. It is formed by having the rabbet on only one board, and that rabbet is the full width of the mating board. The depth of the rabbet is usually at least one half of the width, and the deeper it is made the less end grain will be visible. Taken to an extreme, the depth can be such that only a thin veneer strip remains to cover the width of the mating board, but then the joint is almost a butt joint since the rabbet lip no longer provides structural support, only an aesthetic veneer to cover end grain.
When both pieces recieves a rabbet it is referred to as a double-rabbet joint.
Mitered rabbets provide the appearance of a mitered corner, while providing positive registration for easy clamping and assembly. Once assembled, this joint also provides additional resistance to shear and racking.
To construct mitered rabbets, one board receives a rabbet that has a depth that is (usually) half its thickness and a width the full thickness of the mating board. The mating board would have a rabbet which is the same as its mate's depth, but only half the width. The remaining tenon is mitered.
A further variation with a mitered rabbet is to introduce dowels or biscuits to further lock the two boards together. Drilling perfectly aligned holes is not possible without a jig or appropriate boring machine, but if it is available the creation of the required holes is a simple process. The benefit the dowels provide is positive registration during the assembly and glueup phase, and it also adds considerable resistance to joint separation.
If one rabbet is cut with an angled shoulder and the other board with a matching angled cheek, the two boards join with a dovetail shaped joint. This is slightly more resistant to racking than a conventional rabbet joint.