The plural demonstrative meaning 'those' or 'they', used for things or people that are distant from both speaker and listener (plural of あれ).
あれらはみんな外国から来た学生です。
Those (people) over there are all students from abroad.
棚の上にあるあれらは全部古い本だ。
Those on the shelf are all old books.
あれらをどう処分するか、早く決めないといけない。
We need to decide soon how to dispose of those (things).
あれらは近寄って見ると意外と小さい。
Those, when seen up close, are surprisingly small.
An archaic (and somewhat derogatory) use referring to one's equals or inferiors as 'they'. Considered old-fashioned or rude in modern use.
昔の文に『あれらは城に逆らいし者なり』とある。
An old text says, 'They were those who rebelled against the castle.'