GENERAL INFO

Leurs is a possessive adjective meaning "their". It always precedes a *plural* noun, indicating that multiple people own multiple items.

USAGE

It's used when the owners are plural and the owned item(s) are also plural.

For example: "Ils aiment leurs parents" (They love their parents).

It agrees in number with the *noun it modifies*, not the owner: "leurs voitures" (their cars).

TRAPS

Do not confuse leurs (plural possessive adjective) with "leur" (singular possessive adjective, e.g., "leur livre" - their book).

Also, "leur" can be an indirect object pronoun (e.g., "Je leur parle" - I speak to them).