Mass Air Flow or Mean Air Flow sensor, basically a little wire that changes resistance with the air speed over it and from which the ECU can then compute air flow.
Its a little black box that sits just beyond the airbox in the 2.8s, DO NOT UNDO THE SCREWS ON THE SIDE OF IT TO GO EXPLORING. this breaks contacts inside the maf and your in a hole world of hurt.
Any MAF fitted to most EFi nissan vechiles with a pink sticker from about 96 to 00 is the same as the 2.8 GU. RB25DETs, 26s, 20s ect have the same MAF.