also: GT counter · counter trey · counter · guard-tackle counter
A counter with two pullers, a guard and a tackle. GT counter and counter trey usually name that play, although some staffs change the second puller.
GT counter is named after who pulls. The backside guard pulls and kicks out the end man on the line, and the backside tackle pulls behind him and wraps up through the hole onto a linebacker. Everybody else blocks down, and the back takes a counter step away before running to it.
Naming a play after its pullers is unusually informative, because it tells a lineman his job from the call itself. That is the same idea as a numbering grammar, applied to two positions instead of all of them.
guard-tackle countercounter trey, power, dartCounter trey is the older and better-known name and in most rooms it means the same play. Where it does not, the difference is which second body pulls: some staffs use trey for a version where the second puller is an H-back or tight end rather than the tackle, which changes who is left protecting the backside.
So the useful answer to "are they the same play" is: usually yes, and the thing to check is who the second puller is rather than which name is being used.
counterGT counter"Counter" on its own is nearly meaningless across programs, because almost every offense has one and they are blocked differently. The pullers are what identify it.