Set - Flop a Set - Trips
1) Set: three of a kind where you have a pair hidden and one more exposed
2) Flopping a Set: having a pocket pair, and hitting one of your pair on the flop.
For example, you hold 88 and the flop is 872.
3) Turning a Set / Rivering a Set: hitting your card on fourth or fifth street.
4) Trips: three of a kind where two are exposed and one is hidden.
For example you hold 87, and the flop is 882.