If something catches on, it becomes popular... people start using or following it. It could be related to technology, fashion, slang phrases, etc.
1. It took no time at all for Facebook to catch on in Brazil and surpass Orkut. It practically happened overnight. In fact, all forms of social media caught on really quickly here.
2. Do you think it’s easy for anyone to make up (“invent”) a new phrase and make it catch on so that the whole population starts using it? Perhaps social media helps to spread the word much easier these days.