EBCDIC (Fully, "Extended Binary Coded Decimal Interchange Code") is a character encoding used on IBM mainframes and AS/400s. It is descended from punched cards. Outside of such IBM systems, ASCII (and its decendants such as Unicode) are normally used instead; EBCDIC is generally considered an anachronism.
EBCDIC takes up eight bits, which are divided in two pieces. The first four bits are called the "zone" and represent the catagory of the character, whereas the last four bits are the called the "digit" and identify the specific character. There are a number of different versions of EBCDIC, customised for different countries.