welding vs spot-welding

welding and spot-welding both are nouns.

Word	Noun	Adjective	Verb	Adverb
welding	Yes	No	No	No
spot-welding	Yes	No	No	No

As nouns, spot-welding is a hyponym of welding; that is, spot-welding is a word with a more specific, narrower meaning than welding:

welding: fastening two pieces of metal together by softening with heat and applying pressure
spot-welding: creating an overlapping joint by welding at small points

Other hyponyms of welding include butt-welding, butt welding, spot welding.

welding (noun)	spot-welding (noun)
fastening two pieces of metal together by softening with heat and applying pressure	creating an overlapping joint by welding at small points