Groove Briefs are competition underwear worn in the deadlift and squat.
They have 3 benefits:
1- Give support in your hips.
2- Helps get your suit over your butt.
3- And, last but not least, in the rare case of a suit blow out they prevent your balls from shooting out your suit and in the face of an unexpecting spectator .
I have no idea what is legal in a "raw" meet because I, along with 98% of the rest of the powerlifting world, do not compete that way.