Trust Flow / Citation Flow
Trust Flow and Citation Flow are the two numbers Majestic puts on every domain. Citation Flow is a rough measure of how many links point at the site, weighted by the links pointing at those. Trust Flow measures how close those links are to a set of hand-picked trusted seed sites. Both run from 0 to 100.
The ratio is what experienced buyers look at. A domain with Citation Flow 40 and Trust Flow 30 has links from decent places. A domain with Citation Flow 40 and Trust Flow 5 has a lot of links from junk, which usually means it was spammed or was part of a link network.
They're Majestic's opinion, not Google's, and they can be gamed. But alongside Ahrefs' Domain Rating and Moz's Domain Authority, they're the vocabulary the expired-domain SEO crowd uses, and if you sell to that crowd you need to speak it.