As I am building websites in a government department, it is quite common to hear "Is this site 508 compliant"? Most people in corporate do not know what 508 is about, but in government, 508 makes developers pulling their hair every day.
508 compliance is to let disabled people view websites and low end browser (e.g. text-only browser) display content correctly. If a page displays image, that image must have alternative text to show text information about that image. So disabled user can use screen reader to "view" the page.
508 was made a decade ago when Internet was supposed to display content, not for interaction. Nowadays, 99% of people will not use text-base browser. 508 seems out-of-date now.