One of the many Yiddish words that have made it into English. Most often, 'yenta' refers to a female gossip. (It can also refer to a male, but that's unusual.) This might apply to anyone from a malicious rumour monger to simply an overly talkative person.
It is sometimes also be used to refer to a person who can't keep a secret, or just can't keep their mouth shut.
And it can also refer to a person of low origins or vulgar manners. Also a shrew, a shallow person, or a coarse person.
Pronounced like it looks, YEN-ta. It can also be spelled yente. Yenta was originally a given name, used as a first name for girls. It was originally Yentl, the root word of which meant gentile or kind.
See also: yachna, yideneh, and the most famous yenta of them all, Yenta Telebende.