Purchase intent, attention and clarity, each averaged across everyone who saw it. On their own the numbers mean little. Run two versions of the same ad and the gap between them tells you which to spend money on.
In the tool's own validation testing, a clear benefit-led advert scored 4.22 for purchase intent against 2.96 for a deliberately jargon-heavy version of the same product, and 7.84 against 4.92 for clarity. It notices the difference.