Boozing is the drinking of alcohol, especially a lot of it, or doing it often. It names the activity, not one drink: He's been boozing all weekend means he has been at it for hours or days, not that he had a glass of wine with dinner. The tone is informal and a little blunt; it can sound like a joke among friends, or like a warning if you say someone has a boozing problem. It is the -ing form of the verb booze, so you will also hear people booze as a verb, though the noun booze (the drink itself) is more common than the verb.