The bits number of a processor represents the size of a word.
The number of bits in a word (the word size, word width, or word length) is an important characteristic of any specific computer architecture.
It determines how big the memory can be (ie how big the memory offset number can be). See memory size
The size of a word is CPU-specific.
The computing world is in transition from 8 bit, to 16 bit, to 32-bit to 64-bit computers.
The only limitation imposed is by the 32-bit or 64-bit mode of the process.