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