A poker tie is a term referring to a situation in which two hands have the same value. If this happens, the pot is usually equally divided between the players with the strongest tying hands.
For example, with three players going all-in on the river, the community board reads A, A, Q, 9, 2. You and one opponent both have an A, Q, while the third player has pocket nines.
Although all three of you have a full house, you and one opponent have the same-valued winning hand, so you two are tied, and you split the pot. The third player goes home empty-handed.