Meaning of A4 in English

A4

[noun] [U], [adjective] [not gradable] - (paper) of a standard size used in Europe, measuring 21 centimetres x 29.7 centimetresThe printer has run out of paper, could you get me some more A4?I must get this letter written - have you got a sheet of A4 I could use?A4 paper is twice as big as A5 and half the size of A3.Is this paper A4 or something else?

Cambridge English vocab.      Кембриджский английский словарь.