There is a sensor to measure "Mass Air Flow" so the cars computer can adjust fuel flow to the engine to meet the proper demand.
The MAF sensor has a range of low to high voltages (usually within a range of 0.5 -5.0 volts for most cars) it sends to the cars computer. Your cars computer will compare the voltage the MAF is sending to a reference voltage (usually 5volts for the reference) and the computer calculates the airflow and determines how much fuel needs to be injected.
If your cars computer "sees" a voltage that is out of range, it sets an error code and usually runs a richer mixture just to make sure the vehicle will run.
The voltage error could be caused by a short in the wires to or from the MAF or a bad MAF sensor or a bad (though unlikely) computer or a dirty/blocked airfilter or a dirty sensor.