In poker, “bottom pair” or “bottom set” refers to having the lowest possible pair or set among the community cards on the board.
For example, if the board is K-7-4-3-2 and a player holds K7, they have “bottom pair” with a pair of sevens. Similarly, if a player holds 44 and the board is K943J, they have “bottom set” with a set of fours.
Bottom pair and bottom set can be vulnerable to higher pairs and sets, so players must use caution when playing them.