A short way to say “contact me” — text me, message me, call me. It stands for hit me up, a casual American phrase that already meant “get in touch”. You see it in texts, on Instagram, on Discord, wherever people write fast. HMU if you’re free later. Going to the night market, HMU. It is warm and informal: an open door, not an order. The hit is not a punch; nobody is being hit. Hit up, in this slang, just means “reach me”. It does not belong in an email to a teacher, a job application, or anything that needs a suit. Though actually, even among friends it can sound a little dated now, like something from an older social-media year — but everyone still understands it, and it still does the job when you want a reply without writing a whole sentence.