A flare is a sudden burst of light. The flare of a lit match in the dark night is strangely beautiful.
The flare of a flame in the dark is sudden and bright, and the flare of an idea or emotion is similarly intense. A part of clothing that grows wider, like the hem of jeans that flare — and are also called flares. The verb flare also means to burn brightly or suddenly erupt, like a skin rash that flares up in hot weather or your friend's temper that flares when people tease her about her favorite team losing the big game.