A great fire, or something that has the brilliant quality of fire, literally or figuratively. ("..going out in a blaze of glory.." "..the blazing sun..")

Or, a mark made on a tree to mark a trail, generally a straight horizontal line carved in with a knife, though more complicated patterns denoted different trails or types of trail or hazards ahead. Thus: a trailblazer was originally someone who was the first to walk and mark a trail. A blaze can also be just a general marking, ie, a thin white marking on a horse's head is a blaze.