Butt welds are to groove welds as apples are to pies. (Sorry about the SAT flashback).
A butt weld is a joint between two members aligned approximately in the same plane. Versus - corner weld, tee weld, lap joint, etc.
A groove weld is a weld made in a "groove" between the two members (i.e. beveled plate edges). Versus - fillet weld, plug welds, etc.
(Definitions from ANSI/AWS A3.0)
SO a butt weld may be a groove weld, but not necessarily and a groove weld may be a butt weld, but not necessarily.