There are 17 weight categories universally recognized. There is a proposal to unify all names as some divisions are called differently by some groups and this by itself creates confusion. The 17 categories are:
Every fight is scheduled to a certain weight category . For a fight to be recognized under such weight category, both boxers must make the weight within the limit of the division in the official weigh-in ceremony
Catchweight – This term is used for specific agreements reached by the 2 fighters and is an exclusive commercial contract which has nothing to do with the regulations of boxing.
There are 2 scenarios in which catch weight fights have been scheduled:
A-. World title fight scheduled to x division in which the fighters agree to have a limit of how much they can weight . For example a fight scheduled at welterweight which the limit is 147 lbs. and the fighters agree on weighing 144 maximum. For boxing regulation the fight is within the 147 category, so it is an official welterweight fight.
B-. Over or Under the weight non-title fight. There have been numerous cases where a world champion participates in a fight outside of his / her weight category. Most of the times it is an over the weight fight in which fighters agree on a specific weigh limit.