To relight means to light something again after it has gone out. When birthday candles blow out during the song, you might need to relight them so the birthday person can make their wish. When a pilot light goes out on a water heater or furnace, someone has to carefully relight it to get the appliance working again.

The word applies to any flame or fire that needs to be started a second time. A camper might relight a campfire in the morning using the embers from the night before. Stage crews relight the footlights between acts of a play. Even a tiny flame, like the one on a candle or a match, can be relit.

You'll also see this word used metaphorically, like when someone talks about relighting their enthusiasm for a project they had set aside, meaning they're rekindling their interest and energy. But the literal meaning of starting a flame again remains the most common use.