Severity describes how serious a kind of issue generally is. It is a fixed property of the issue type itself — a missing H1 heading is always a medium-severity SEO issue, and a page returning a server error is always a critical technical issue, regardless of which specific page it happens on.
Severity isn’t the whole story
Priority is different: it is how strongly webioom recommends acting on one specific finding right now, relative to everything else in the report. Priority takes severity into account, but also how widely the issue is spread — how many pages it affects, and whether one of them is your homepage.
A medium-severity issue on one rarely-visited page and the same medium-severity issue across your homepage and eleven other pages are not equally urgent. Priority is what tells them apart; severity alone can’t.
Why the distinction matters
Reading severity in isolation risks over-reacting to a rare edge case or under-reacting to something small but everywhere. Priority exists specifically to answer the practical question a severity label alone can’t: out of everything in this report, what should I actually look at first?