A slut is a mean word for a person, usually a woman, who has a lot of sex with different people.
The word slut is very mean and rude. It is not a nice thing to say to someone.
Examples:
She called her a slut because she was mean.
He said she was a slut, but that's not nice.
The girl was sad because someone called her a slut.
He's just a mean person who calls people sluts.
I heard someone say she's a slut, but I don't believe it.
She's not a slut, she's just nice to everyone.