Domain Authority (DA) is a score that predicts how well a website will rank in search results. It ranges from 1 to 100 — the higher, the stronger your site's authority.
Domain Authority is a third-party metric (not a Google factor) that estimates ranking strength based mainly on your backlink profile.
No, it is a third-party metric. But it correlates with ranking strength.
It depends on your niche; compare against your direct competitors.