高抬贵手 is a polite four-character idiom (chengyu) used to plead for leniency or forgiveness. Its literal meaning is 'to raise your noble hand' — the image is of someone lifting their hand to spare you from punishment. You say it to someone in a superior position (a boss, a teacher, an official) when you have made a mistake and want them to be merciful and not apply the full penalty. It is formal and carries a respectful, humble tone.