What is exactly does it mean when someone says "memory-mapping","IO Mapping","Memory Mapped IO" & "Port Mapped IO"?
I think these terms are primarily used with microprocessors, rather than microcontrollers.

"Memory-mapped" I/O devices just appear as normal memory locations, and can be read or written by any instructions that can read or write normal data memory.  Memory-mapped I/O can be used by any microprocessor.

Some microprocessors (Intel 8085 and relatives) have a separate address space for I/O device use, not part of the normal memory space, and a limited number of instructions to read from, or write to that address space.  I/O devices using this space would be "IO Mapped".