they

Concise Oxford English Dictionary © 2008 Oxford University Press:
they/ðeɪ/

▶pronoun [third person pl.]

• 1 used to refer to two or more people or things previously mentioned or easily identified.

  ■ people in general.

  ■ informal people in authority regarded collectively.

• 2 used to refer to a person of unspecified sex (in place of either ‘he’ or ‘he or she’).

– origin ME: from ON their, nominative pl. masc. of sá.

usage: It is now widely held that the traditional use of he to refer to a person of either sex is outdated and sexist; the alternative, he or she, can be clumsy. It is now generally acceptable, therefore, to use they (with its counterparts them, their, and themselves) instead. This is especially the case where they follows an indefinite pronoun such as anyone or someone (anyone can join if they are a resident). In view of the growing acceptance of they, it is used in this dictionary in many cases where he would have been used formerly.