Source : Free On-Line Dictionary of Computing

command interpreter
     
         A program which reads textual commands from
        the user or from a file and executes them.  Some commands may
        be executed directly within the interpreter itself
        (e.g. setting variables or control constructs), others may
        cause it to load and execute other files.
     
        {Unix}'s command interpreters are known as {shell}s.
     
        When an {IBM PC} is {boot}ed {BIOS} loads and runs the
        {MS-DOS} command interpreter into memory from file COMMAND.COM
        found on a {floppy disk} or {hard disk} drive.  The commands
        that COMMAND.COM recognizes (e.g. COPY, DIR, PRN) are called
        internal commands, in contrast to external commands which are
        executable files.
     
        (1995-03-16)