Flattery is excessive praise. If you're hoping to borrow your brother's car, be careful not to overdo it when you compliment his haircut, new shoes, and singing voice — he knows flattery when he sees it.
As opposed to real praise, flattery is insincere and almost always has an ulterior motive. The Old English root word of flatter is flater, which originally meant "to stroke with the hand or caress." When you stroke someone's ego to get what you want, you're using flattery. If the person you are wildly complimenting tells you that flattery will get you nowhere, you know it's time to back off.