Please help '00 Jetta GL P0172 error code

Just got the dreaded check engine light and found out it was P0172 engine running too rich. I saw on another thread that it is the MAF. Sorry for my ignorance, but what is an MAF? Are there any other solutions to the problems? Could it be a bad O2 sensor? Thank you.

pull up the engine cover and check the 1/4" vacuum line for the fuel pressure regulator on the intake maifold, it normally cracks and causes a system too rich code.

Also pull off the intake pipe from the throttle body and check for lots of oil/carbon residue on the throttle body.