Catch on: to become fashionable or popular；to understand, especially after a long time. As in I wonder if the game will ever catch on with young people? He doesn’t take hints very easily, but he’ll catch on (to what you’re saying) eventually.
中文释义：catch on有两层意思：1. （something） catch on，某个东西流行起来，变成时尚；2. （someone）catch on， 某人能够理解，明白，学会。 一个东西只有变得流行，成为大众时尚（catch on），才能被人们所记住，理解（catch on）。例句1：We were teasing Jim, but he was slow to catch on that we were joking；例句2：Online trading has been slow to catch on in this part of the country.