Source : Free On-Line Dictionary of Computing

program counter
     
         (PC, or "instruction address register") A
        {register} in the {central processing unit} that contains the
        addresss of the next instruction to be executed.  The PC is
        automatically incremented after each instruction is fetched to
        point to the following instruction.  It is not normally
        manipulated like an ordinary {register} but instead, special
        instructions are provided to alter the {flow of control} by
        writing a new value to the PC, e.g. JUMP, CALL, {RTS}.
     
        (1995-03-21)