干吗 (gàn má) is a colloquial variant of 干嘛 (gàn má), meaning 'what are you doing?' or 'why?' in spoken Chinese. It functions as a verb-phrase question, used to ask about someone's action or the reason for an action. You can use it directly at the end of a question or before a verb: 你干吗？ ('What are you doing?') or 你干吗不去？ ('Why aren't you going?').