Your MAF measures two things, well three if you factor in the IAT's. Otherwise those thermistors in the MAF measure the volume of the income air, as well as the speed (or velocity) of the incoming air (as PGA mentioned). Generally that is done in Hz.
Our stock MAF is a drop in module that has a non-aerodynamically friendly chunk of plastic that extends into the center of the airflow. INside this plastic chunk is the thermistors that measure the quantity and speed of the incoming air flow. Ours is very similar to the 3800 V6 engines both N/A and Supercharged.
Here is ours;
An LSx style MAF however, is a full bore MAF with an aerodynamic center seperator and has it's thermistors exposed to the income airflow (for more accurate, quicker readings). Most tuners in the country that tune GM V8's do LSx's, and hence are very well experienced in LSx tuning of MAF's.
Here is an LSx style MAF;
Hence why I was curious.