catch (sb / sth) up: QUALITY to reach the same level or quality as someone or something else
catch up: to learn or discuss the most recent news
catch up on / with sth: to do something that you did not have time to do earlier
catch up with sb: If something bad that you have done or that has been happening to you catches up with you, it begins to cause problems for you.
catch on: BECOME POPULAR to become popular
catch on: UNDERSTAND informal to understand something, especially after a long time
catch sb about: to trick someone so that they make a mistake
(sb / sth) up: REACH to reach someone or something that is in front of you, by going faster than them