A skylight is an opening in a roof assembly that is permanently covered with a translucent or transparent material to allow the sunlight into the building. Skylights differ from heat and smoke vents in that they are inoperable and only serve the function of allowing light into the building.

A skylight that is FM Approved has been evaluated to verify that only the sunlight gets through the skylight. The vigorous evaluation process includes performance testing for fire, wind, wind borne debris, degradation due to sunlight, hail and impact.