Three of a kind
If in a hand, a player receives three cards of the same kind, then s/he is said to have three of a kind. For e.g. if a player gets an A-4 when the cards are dealt out, and then the community cards show up as A-3-A-9-K on the board, then the player has three Aces giving him a three of a kind.
However, in Texas Hold’em, a trips or set is only considered if the player holds a pair in her/his hand cards with the third card appearing on the board. However, in other variations of poker that may not always be required.