ASTM D2859 or the methenamine pill test, is also called the Standard Method for Ignition Characteristics of Finished Textile Floor Covering Materials. This pass/fail test measures the size of the burn to determine flame resistance of textile floor coverings. — simply put: does it burn?
A methenamine tablet (or pill) is ignited on the tested material, simulating a scenario that would be similar to if someone dropped a lit cigarette on the floor.
It is required for all carpet sold in the United States.
Note that this is different than the actual flame spread of the carpet or floor covering.