"Catches on" is a phrase that can be synonymous with "popular" or "trending". Similar phrases that can be used include "takes off", "spreads like wildfire", "becomes a sensation", "gains traction", or "goes viral". When a product or idea catches on, it gains momentum and interest among a wider audience. This can lead to increased sales, attention, and even cultural significance. The opposite of "catching on" would be "fading away" or losing momentum. In the world of social media, catching on is often seen as a measure of success - making it important for businesses and creators to create content that is shareable and easily catches on.