Something that's false is wrong or untrue. If you spread false rumors about a friend, you're telling lies.
When you read a fact in a textbook that you know is mistaken, you can describe it as false. Giving someone a false impression about your family's pizza place — implying that it's a fancy restaurant when it's really a take-out counter and a pizza oven — means you're giving the wrong idea. False can also mean "fake," as in false eyelashes or a false smile. It comes from the Old French fals, which is faux in Modern French: "false,fake, incorrect, or mistaken."