I am not asking for the "Level A: Meets all level A standards" definition (which is completely useless to anyone other than lawyers or software developers.)
I need the ones about each level that conveys an idea of their usefulness so that I can better describe why increased levels should be strived for.
I swear I once found one that came straight from W3C but I have been searching for days now and I can't find it again.
Not sure if this is what you are looking for, but it's from the Section508.gov website:
Level A (minimum) – Addresses the most basic web accessibility features, but does not generally achieve broad accessibility.
Level AA (mid-range) – Addresses most common barriers for disabled users and aligns to the Revised 508 Standards
Level AAA (highest) – Addresses the highest level of web accessibility, but is not recommended as a general policy, because it is not possible to satisfy all criteria for some content.
https://www.section508.gov/content/build/website-accessibility-improvement/WCAG-conformance