Moz and Ahref have set up their SEO metrics. Moz call it "Domain Authority" whereas Ahref call it as "Domain Rating" which shows strength of a given website’s overall backlink profile. Both the tools rate Damain on the scale between 1 to 100, 100 is considered the best. DA above 40 and Dr above 70 is considered a good score. Try to get backlinks from sites that have DA/DR above mentioned numbers.