Our experiences over the past nine years show that 50,000 is a difficult but doable goal, even for people with full-time jobs and children. The length makes it a short novel. We don't use the word "novella" because it doesn't seem to impress people the way "novel" does.
We define a novel as "a lengthy work of fiction." Beyond that, we let you decide whether what you're writing falls under the heading of "novel." In short: If you believe you're writing a novel, we believe you're writing a novel too.