Does it do anything special? For example T-Bolt and Ice Beam together on a Blissey.
The Bolt beam combo is where a pokemon has both the moves thunderbolt and Ice beam in their moveset. This is a combo largely used because ice and electric together provide great neutral coverage (along with a ghost and fighting move this gives super effective coverage to almost every Pokemon in the game).
The type coverage checker tool
a combination of thunderbolt and ice beam or any other electric and ice moves.