Definition of dominated
In poker, we are dominated when our opponent has a common card with us, but his other card is stronger than ours. For example, we'll say that AK dominates AQ or KJ dominates KT. When you're preflop with a dominatedth hand and you're all in, your equity will usually be 25%. We could also use the expression if you have a pair of 8s with a pair of preflop meeting a pair of 9s, but generally, given the huge equity gap, we would say that there are crushed of you in that situation (with an equity of less than 20%).
Dominated after the flop
We can also use the expression dominated to talk about a situation postflop. Usually, when we talk about a dominatedth hand, it will be during an all in when 2 hands are all in. You push your mat with AQ on A23 and your opponent calls with AK; here you are dominated. The closer you get to the river, the more disastrous your equity will be. AK vs. AQ preflop will give AQ 25% equity. At the flop, about 14% if the hand has not improved and at the turn, 7%. At the turn, not only are there dominated of you per AK, but also, given your equity, there are crushed of you!