On HP Printers..what does E/AO designate?

I've got a buddy who needs to download a driver for a printer and apparently has a choice between his obvious printer type and the same printer with "E/AO size"' as an option.

What does this mean?

I'm not absolutely sure but I think it refers to paper sizes used in Europe and elsewhere. Here we call it letter or legal etc. In Europe it is A1, A2 etc.