Although specific meanings vary from country to country, I will attempt to produce an exhaustive list here.
1) A generic term for achieving an advantage in a sports game (verb, occasionally noun).
2) An amount due; a debt (noun).
3) A grievance that is harbored and requires satisfaction (noun).
4) A group of 20 items (noun).
4a) The amount of 20 pounds (noun)
5) The act of securing an advantage, especially a surprising or significant gain (noun).
6) The act or an instance of buying illicit drugs (noun-verb).
7) A successful robbery (noun).
8) A sexual conquest (noun-verb).
8a) Kissing someone, esp French kissing
them (noun-verb, largely Irish-centric slang).
9) An exclamation of pleasure when learning of good news.