To "catch on" means to become popular. You use this phrase when you're talking about ideas, books, comedians, food, products, and anything that lots of people can like.
The phrase "catch on" refers to the beginning of the situation, when people first start to be interested and think that something is popular. After something "catches on", you just say that "it's popular":
It's super popular now, but it actually didn't catch on until the third season.
The past tense of "catch on" is "caught on".