Indirect
  Two forms - Memory and Register

  The register or memory specified in operand contains the effective
    address to be accessed.

    8086: CALL AX   # register
    ARM:  LDR R1,[R2] # load R1 from memory addressed by R2, full 4GiB range.
      Very common in RISC

    6502: JMP($2000) # memory
      Memory indirect common in older CPUs with limited registers.

    Many of the IBM 360 architecture instructions use base (indirect) 
     addressing. Makes relocation of code simpler.

  Basically a pointer to memory of interest.

  RISC architecture relies heavily on Register Indirect to provide access
    to full memory range since operand size is often smaller than address 
    range.