to destroy something completely with fire or heat, or to be destroyed completely by fire or heat: Meteorites often burn up in the atmosphere before they reach the ground.

From Longman Dictionary of Contemporary English burn up phrasal verb 1 if something burns up or is burnt up, it is completely destroyed by fire or heat The satellite will burn up as it re-enters the Earth’s atmosphere. burn something ↔ up Most of the woodland has now been burnt up. 2 burn something ↔ up informal to use a lot of something in a careless way Most household appliances burn up loads of electricity.