the official stance of arXiv is that it is intended for papers that are finished and ready for submission to peer review, i.e. the authors believe it's finished

the official stance of arXiv is that it is intended for papers that are finished and ready for submission to peer review, i.e. the authors believe it's finished and publishable. in a practical sense, most people don't think of it this way though. putting something on arXiv means "i want people to be able to cite this, and for it to show up on Google Scholar", which might include works in progress, short notes, or lots of other things that don't fit the official criteria.