The definition of the character that's produced by each key on the keyboard. The layout is different for different countries. The UK and the USA use the QWERTY standard (defined by the top line of characters on the keyboard), while France uses AZERTY, and other countries incorporate accents and special characters. In order to use your computer when typing in a different lanuage you need to change the keyboard layout and the font that's used. Both are defined by the codepage. You can change the properties of the keyboard by opening the Keyboard icon in the Control Panel.
