Burn, scorch, char, sear, singe mean to injure by exposure to fire or intense heat.
Burn is the most comprehensive of these terms, for it is applicable regardless of the extent of injury or of whether fire or heat is the destructive agency. Burn is also applicable when a similar injury or effect is produced by another agency.
Scorch implies superficial burning that changes the color (especially to brown or black) or texture of something.
Char usually implies total or partial reduction to carbon or charcoal by fire.
Sear applies basically to the burning or scorching of animal tissues by fire or intense heat (as in cauterizing a wound, branding an animal, or quickly browning the outside of meats so that they will retain their juices in later and slower cooking).
Singe implies a very superficial burning. Sometimes such burning is intentional, especially when the short hairs or bristles covering a carcass being prepared for market or for cooking are quickly destroyed by a flame.