First, there's parallel flash. Parallel flash on PC mainboards has an address bus which is between 17 and 19 bits wide and a data bus which is 8 bits wide.
Bigger address busses are sometimes used; x16 flash is also sometimes used (and shared data/address busses, too).
I agree you don't see these often on x86 PC boards though ;-)
CFI is the Common Flash Interface as developed by Intel and friends and published by Intel.
Developed by AMD, Intel, Sharp and Fujitsu; published by AMD says my version of the doc (maybe all vendors publish their own, dunno).
CFI covers both 8-bit wide and 16-bit wide flash.
And 32-bit wide. Not that you'll likely ever see that on an x86 PC :-)
Segher