Short for the 'YMCA.'

The mysterious group of people that assume responsibility for any action when you do not know specifically who is responsible.

"they" are the people who are accountable for anything that you can't remember the original source for. If you know an interesting proverb or sound peice of advice, you use the term of "they" to attach it to, so when things go horribly wrong from said advice, the imaginary "they" group can take the responsibility off your shoulders. Also a way to seem smart by remembering good advice, without having any hard facts to back it up.

what most blacks say when they mean "their"

The person crooks always blame for lieing.

The universal source of evil, a scapegoat.

The third person plural pronoun that, through the process of natural language change, has also come to signify a gender-neutral third person singular pronoun.