Butt Edge Joints

The three cornerstones of edge joints, commonly referred to as "butt joints" are the Edge-To-Edge, Edge-To-Face, and Face-To-Face.

Each of these joints are formed by when each piece of wood is machined straight and square before being fixed to its mate.

Edge-to-edge - Where the narrow surface of one piece is joined to the narrow surface of another piece. These joints are commonly used to create wide boards out of smaller pieces.
Edge-to-face - Where the narrow surface of one piece is joined to the wide surface, or face, of another piece. These joints are often called corner edge joints since they are used in connecting the columns or vertical components of cabinets to each other.
Face-to-face - Where the wide surface, or face, of one piece is joined to the face of another piece. These joints are primarily used to create thicker pieces of wood from thinner stock. You would use these joints to form bedposts or thick table legs.