That which belongs to them; the possessive case of they, used without a following noun.
Belonging to, from, of, or relating to, them (plural).
‘they will meet tomorrow at their convenience;’; ‘this is probably their cat’;
used to refer to a thing or things belonging to or associated with two or more people or things previously mentioned
‘a favourite game of theirs’; ‘they think everything is theirs’;
Belonging to someone (one person, singular).
misspelling of there
The possessive case of the personal pronoun they; as, their houses; their country.
‘Nothing but the name of zeal appears'Twixt our best actions and the worst of theirs.’;