Trump has two main meanings:

1. To trump something means to beat it or surpass it with something better. When a new discovery trumps an old theory, it proves the old idea wrong. If your sister suggests going to the park but you trump her idea by proposing the water park instead, you've topped her suggestion.
2. Trumped-up charges are false accusations against someone who didn't actually do the things they're accused of. Sometimes these are completely made up accusations, and sometimes they're exaggerations of real facts.
3. In card games, a trump is a special suit or card that is chosen to be more powerful than the others, so it can win over higher cards from other suits.