1. To become popular.
2. To understand, usually after some initial difficulty; SYN. get onto, tumble, latch on, cotton on, twig, get it.
3. When a fashion or habit becomes popular and is adopted by many people, it catches on. When a product or service becomes popular and is used or bought by many people, it catches on.
4. When you eventually begin to understand something or begin to learn a skill after practicing and studying, you catch on.