Fillet brazing (also called 'bronze welding') is well known in framebuilding. But when extra pieces are added and are welded together to form smooth countours and whathaveyous (sometimes even looking like lugs), these are called 'bilaminates'.
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One of the pioneers in bilaminate frame construction was Claud Butler in the 1940s and 50s. He called it "the greatest advance in frame building since the evolution of the 'safety' bicycle."

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This bike looks big (it's 23"/58.4cm c-c, w/ a 23.5"/59.7cm TT) but it's the equivalent of a modern 19 or 20" frame size. The reason sizing was really goofy on some early-80s MTBs was they were built around 180mm long seatposts (instead of 300mm or more on modern bikes). When you found your correct size it was about like a road bike, except that the BB was so much higher that the long headtube and seattube had the 'giraffe-milker' look to it.