Extended Binary Coded Decimal Interface Code

EBCDIC, the Extended Binary Coded Decimal Interface Code, is an eight-bit binary format used by various IBM mainframe operating systems.

a character set IBM uses on mainframes

EBCDIC is a character set IBM uses on mainframes, so you'll probably only come in contact with EBCDIC if dealing with legacy business applications.

a similar standard which stands for Extended Binary Coded Decimal Interchange Code called EBCDIC

IBM created a similar standard called EBCDIC which stands for Extended Binary Coded Decimal Interchange Code.

an IBM code for representing characters as numbers

Pronounced eb-sih-dik, EBCDIC is an IBM code for representing characters as numbers.