Butt Joint
From DT Online
A Butt Joint is a simple coming together of two edges or faces. The joints can be fixed by simply gluing but more often is reinforced or strengthened before doing so. Butt Joints can be used to widen boards, make frames and create carcasses.
Note:
When used to widen boards, Butt Joints are quite often simply glued and this is known as a Rubbed Joint.