What is a metal film resistor?
As the name indicates, the metal film resistor is made by depositing a thin layer of metal onto a ceramic former. The metal film acts in the same way as resistance wire, and as the thickness, width and length can be accurately controlled, the metal film resistor can be produced to a high tolerance.
Also as the metal film resistor can be pre-aged and the metal protected to ensure it does not degrade over time, the long term stability is good.
The metal film resistors are a popular choice these days for leaded axial resistors and therefore they are used in huge quantities.