What's the difference between a preprint and a working paper?
As per the other (current) answer, in fields I know (pure and applied math, computing, GIS, ...) a working paper is less mature than a preprint. However, there is not necessarily a progression from one to the other.

The expectation is that a preprint is basically ready for submission to peer-reviewed journal or other venue, and may even already be submitted by the time anyone else reads it. In some cases, that may not be strictly true: I've seen working papers where there was a specific clear gap or two that still needed to be filled before submission, and I've myself had to rework preprints significantly based on friendly feedback received and/or different format/length expectations where ultimately submitted.

In fields I know, "working paper" carries connotations of work-in-progress. It may still be under active development, or paused to be revisited much later, or maybe never. But someone feels it is worth sharing and having in citable form regardless of any half-bakedness. Nothing wrong with that, and during my Ph.D. I was strongly influenced by a working paper that outlined an approach the author never got around to completing.