Bronze welding is a process of joining metals in which the edges of the metal are heated to a temperature below their melting point and a bronze alloy is simultaneously melted and caused to flow over the edges and join with them. By this means a strong and ductile union is produced between high melting point metals, i.e. cast iron, steel, copper and malleable iron etc.
Bronze welding resembles brazing up to a point, the application of brazing is generally limited to joints where a close fit or mechanical fastening serves to consolidate the assembly.
I draw your attention to the second paragraph, which refers simply to "brazing". If we're talking bike frames, the "close fit or mechanical fastening" referred to would be lugs into which the tubes are brazed. If there's no lug, you're relying on the filler material to hold the tubes together:
In bronze welding the filler alone provides the joint strength
Which is what's also known, although possibly only in framebuilding circles, as "fillet brazing". The extra word "fillet" is important