A triple is the pair idea extended, with one wrinkle that makes it much harder to spot: the three cells do not need identical candidate lists. They need their candidates to be drawn from the same three digits.
So {2,5}, {5,8} and {2,8} form a triple on 2, 5 and 8 — as do {2,5,8}, {2,5} and {5,8}. Between the three cells, all three digits are accounted for, and every other cell in the unit can drop all three.
The practical advice is to look for the three digits first rather than the three cells. Scanning for "which digits are confined to these three cells" is a shorter search than checking every combination of three cells in the unit.