If you are a C++ programmer then you already know pointers. According to WikiPedia a pointer is a programming language data type whose value refers directly to (or "points to") another value stored elsewhere in the computer memory using its address.
The same concept of pointers is used in PLC but named "Indirect Addressing". When an indirect memory address is specified, the designated memory word will contain the address of the memory word that contains the data that will be used as the operand of the instruction.
