From Halopedia, the Halo wiki
An incendiary weapon is a weapon designed to start fires or destroy sensitive equipment using incendiary materials.
Incendiary projector may refer to the following:
United Nations Space Command
UNSC incendiary-based weapons rely on a chemical process between metal powders and oxides to create high temperatures, with no explosion. Commonly, aluminum and iron (III) oxide are used in the reaction; temperatures an upward of 2500 °C (4500 °F).
Covenant incendiary projector weapons uses gel containing a stable yet hazardous chemical mixture containing Caesium. It burns at approximately 2200 °C (4200 °F) and will not burn underwater.