Definition from Wiktionary, the free dictionary
See also a4
Etymology 1 
See the Wikipedia article ISO 216, the international standard on paper sizes.
- A standard paper size, defined by ISO 216.
- dimensions: 210 x 297 mm
- 2001 — Eoin Colfer, Artemis Fowl, p 66
- "There are preparations to be made for our guest's arrival," said Artemis, handing a typewritten sheet of A4 to Juliet.
See also 
Etymology 2 
Proper noun