mug something up

Từ điển Oxford Advanced Learner 8th

ˌmug sthˈup | ˌmug ˈup on sth derived
(BrE, informal)to learn sth, especially in a short time for a particular purpose, for example an exam
•You just need to mug up a few details.
•He's frantically mugging up on Japanese before his trip to Tokyo.
Main entry: ↑mug_derived