Definition of height
In poker, we can talk about "height" when we have less than a pair. For example, if a hand like A2 does not connect with the board, we would say that the hand is "ace height". This hand could beat, for example, a player who has KT with "king high". We can also use the expression to refer to the sidekick. If two players have an ace on A-5-5-6-7, the player with AK will say he has a pair of aces with king high and the player with AJ will have a pair of aces with jack high. These cards that go with another are also called sidekicks.
Ace height, a respectable hand in a head to head
If you play at full ring tables, the idea of winning a showdown hand with "ace high" is a bit far-fetched, but if you're a regular in heads-up games, you know that a hand like ace high is relatively strong. Obviously, if your opponent has shown a lot of strength preflop and on the flop, it's more than possible that your hand is not good, but in the majority of cases where there has been little action, ace-high will be the best hand most of the time. A hand like AT will be the best hand 60% of the time on a 7-7-3-2-3 board against an opponent who would play any two.