It is a subset of something of a value to somebody else and enough so that they are willing to pay you for it, a product, a service. Preferably to pay enough to

It is a subset of something of a value to somebody else and enough so that they are willing to pay you for it, a product, a service. Preferably to pay enough to justify your spent time of course, maybe not right away but at least long term. Even better if not purely digital as it seems we have quite enough of those already.