Josh says this:
Though worded as concisely as a short story, it has room for scenes to breathe. Moments can linger. The fist that squeezes the world of a short story into a few compact scenes can be unclenched a little--bits of backstory let in, descriptions filled out, characters lived with longer. But the novella embraces not too many characters, and not too wide-ranging a plot, not too vast a scope--those are the realm of the novel. A novella compresses the world with a short story's focus, but it explores that smaller space with a novel's generosity. (emphasis added)
Write that down. It's the best definition of "novella" I've ever seen.