PETSCII
Commodore's character set — ASCII plus block and line graphics right on the keys, the basis for the C64's on-screen art.
PETSCII (PET Standard Code of Information Interchange) is Commodore's own take on ASCII, introduced with the PET in 1977 and inherited by the C64. Beyond the letters it carries a whole library of block, line and shade characters printed on the keys, so anyone could draw boxes, borders and figures straight from BASIC without a graphics mode.
That graphic character set made PETSCII an art form of its own: menus, game levels and full pictures built in text mode, often in BBS settings on Commodore machines. It survives as a retro style in modern demos, where the limitation — 40×25 characters and 16 colours — is the whole point.