A stock is just an ownership in a company. The company doesn't even need to be public. You can incorporate and issue yourself a million shares if you want. Then sell some shares to investors who want to speculate that your company will do well in the future.
OP lacks basic knowledge. Instead of taking my advice to look up the meaning of 'stock' he prefers to be ignorant. Its not even that complex
We have to start with the assumption that he's comparing abstractions or there's really no debate.
...and I apologize if this seems like I'm splitting hairs. But "stock" generally refers to the equity shares a company offers to the public.
Investment in private companies is usually via VC firms, angel investors, and large institutions, or from friends & family I guess (depending on size).
Those investments wouldn't typically be called "stock" - and would actually be more like investing in bitcoin than owning stock in publicly traded companies is.