It means that it has acquired a red or white heat when subjected to intense heat. It usually refers to coal or a metal.
It shines, bright white, usually due to the intense heat that puts a metal "to white red". It comes from the Latin in ( "interior, own" ) candens , entis ( "bright white" ) the suffix _scente ( "action , which does" ) .
INCANDESCENT: HOT, ON, FLAMING.