Stands for Hit Me Up.
This word means "i'm bored so you should talk/chill with me".
A word generally used by fuckboys that have no purpose in life other than to convince a perfectly ordinary girl into sleeping with him.
Hit me up mostly seen on Snapchat or Instagram. Normally people say this when their bored and they need to talk to someone. If you see DHMU don't talk to then because their either busy or their not happy