What does their mean in a sentence?

"Their" is a possessive pronoun that refers to multiple people or things that have already been mentioned. It indicates that something belongs to them.

Examples:

* "The children played with their toys." (Their refers to the children.)

* "The cats ate their food." (Their refers to the cats.)

* "The students finished their homework." (Their refers to the students.)

It's important to note: "Their" is always plural and should not be used in place of "his," "her," or "its."