What are wheelchair entrances and why should we care about them? Web Accessibility is making the web more accessible for those with impairments (generalization).
Things like putting aria tags on your hover menus to tell things like screen readers that a menu has appeared, or that the tab has changed, etc. This is such a huge topic that I can't cover in one comment on Hashnode ;)
Check out some of these resources that do it way better justice than I can: