A 301 redirect is a permanent redirect (where a page has been permanently moved from one URL to the other), and a 302 is temporary.
During the English Google SEO Office-Hours From November 5, 2021, someone asked about 302 redirects. (The video below has been queued to the 34-minute, 22-second mark, where the question was asked:
“We've heard that temporary 302 redirects don't pass page link equity.
“Is our understanding of that accurate? In general, we’ve heard that using 302s causes significant SEO issues which has caused us to wonder if we should avoid these at all costs or if there are specific instances where we should use them.”
My Understanding of John’s Response
So, to understand this from an SEO perspective, we have to know the history of how this became such a conflated issue.
I think it really comes down to the fact that 301 redirects tell Google to index the page that’s been redirected to (the one the 301 points to), whereas 302 redirects don’t do that.
If you understand that, it then makes sense that a 302 page would probably still be indexed, and I think that’s where a lot of the confusion and error comes from.