also: ace · ace combo · deuce, trey (the same naming system)
The center-and-guard combination on a nose, named by a numbering system that continues outward: ace, deuce, trey. Not the same ace as the one-back backfield.
2 meanings, all below. Jump to the one you heard.
The center and a guard work together on the down defender between or over them, get him moving, and one of the two comes off to a linebacker. It is a combo block, and ace is the name for the specific pair involved.
What is worth learning is the naming system rather than the single call, because it continues outward: many staffs use ace for center and guard, deuce for guard and tackle, and trey for tackle and tight end. Once a coach knows that, a call he has never heard tells him which two men are involved, which is the same property a numbering grammar gives a play call.
ace combocombo block and double team, scoop block, aceThe same word names a one-back backfield, a set with one receiver split to each side, and the Air Raid's base four-wide formation. All three are formations and live in their own entry; this is a blocking call. Nothing connects any of them beyond the word.
Context resolves it in practice, since this one is said in an offensive line meeting and the others in a formation call, but a new coach hearing both in one week has no way to know they are unrelated rather than faces of one idea.
aceThe ace, deuce, trey naming is common but not universal, and some programs use those words for entirely different pairings or not at all. It is the shape of the system that transfers, not the specific words.