1. belonging to or associated with the people or things previously mentioned or easily identified
Usage: possessive form of ‘they’
2. belonging to or associated with a person of unspecified gender
Usage: used as a gender-neutral singular possessive

Examples

• The students forgot their books at home.
• Their house is painted blue.
• The dogs wagged their tails excitedly.
• Each person should bring their own lunch.
• Their decision surprised everyone.
• The children played with their toys.
• Someone left their umbrella in the office.