Relative strength concerns your maximum effort in relation to your body weight.

A 225-pound person that can push 250 pounds overhead is weaker in this respect than a 175-pound person who can push 210 pounds overhead, even though lifting 40 pounds more. This is often called "pound for pound" strength.

Because it is connected with your body weight, this classification favors people that are of lower body weight. Olympic weightlifting is an example here because the weight of the competitors is considered in tiebreakers. If two lifters end up lifting the same amount of weight, the winner is the one who weighs less.