Yes, the noun 'stuff' is a common noun, a Word for any stuff of any kind.
A proper noun is the name of a specific person, place, thing, or a title; for example:
- Mr. Stuff Warehouse (wholesaler), Northridge, CA
- Good Stuff Diner, New York, NY or Hot Stuff Cafe, San Gabriel, CA
- My Stuff Bags Foundation (charity), Westlake Village, CA
- "The Right Stuff", 1983 movie with Sam Shepard and Scott Glenn
- "Hot Stuff", disco song, singer Donna Summer
