Hagaki paper refers to a paper size setting that can be programmed into most inkjet printers. Any paper size other than the printer's default size setting must be specifically selected prior to printing.
The word "hagaki" is Japanese. Due to the language barrier, some printers do not offer it as an option, instead offering an equivalent size called "Japanese postcard." "Hagaki" translates roughly to the English word "postcard."
Different countries often have different standards when it comes to the standard size for postcards and other mailable documents. The "hagaki" or "Japanese postcard" size setting is the official postcard size recognised in Japan.
Some inkjet printers offer two Japanese postcard size settings: "Japanese postcard" and "Japanese double postcard." The first setting--the standard postcard size--is 10 by 14.8 centimetres. The second is 20 by 14.8 centimetres.