pretend is a verb that means to behave as if something is true when you know that it is not, especially in order to deceive people or as a game.
Common usage examples:
1. She pretended not to see me when I walked by.
2. The children were pretending to be pirates.
3. Don't pretend you don't know what I'm talking about!
4. He's just pretending to be rich.
5. Let's pretend we're astronauts exploring Mars.