Domain Authority is provided by Moz, this metric is at domain level, it meaning that each url/page under one domain will return same value, unlike page authority which is url metric. Both of metrics use logarythmic value from 0 to 100 - more difficult increase DA from 20 to 30, than from 10 to 20.
In Moz opinion: Domain Authority is Moz's calculated metric for how well a given domain is likely to rank in Google's search results.
In real seo world, domains with high domain authority can have Google penalty or can be banned in Google, so you need also check other signals like Majestic TF, Google index, domain traffic or Semrush metrics - which will tell you how many keywords have provided domain in top search results. Especially when you are looking for expired domains and would like a real increase Google ranking of your website.
You can quickly check Moz domain authority typing your domain name bellow and pressing CHECK button.