Толковый словарь английского языка Oxford English Reference - they

pron. (obj. them; poss. their, theirs) 1 the people, animals, or things previously named or in question (pl. of HE, SHE, IT(1)). 2 people in general (they say we are wrong). 3 those in authority (they have raised the fees). 4 disp. as a third person sing. indefinite pronoun meaning 'he or she' (anyone can come if they want to). Etymology: ME thei, obj. theim, f. ON their nom. pl. masc., theim dat. pl. of s{aacute} THE that