A fix-up (or fixup) is a novel created from several short fiction stories that may or may not have been initially related or previously published. The stories may be edited for consistency, and sometimes new connecting material, such as a frame story or other interstitial narration, is written for the new work.
I’d just never heard the term before this article popped up last night. Thought maybe it might be a new thing for some of you, as well!
The early books in the The Utterly Uninteresting and Unadventurous Tales of Fred, the Vampire Accountant series by Drew Hayes are very much like this. It feels very much like someone occasionally journaling a brief adventure they had and I think it pays off in the big picture as you go through the books.