Seo data - what is it?

Any data you use to make SEO decisions. The main pieces are Search Console (queries, clicks, impressions and positions straight from Google), analytics (what people do after they land), crawl data from something like Screaming Frog (broken links, titles, redirects), and keyword and backlink data from tools like ahrefs or semrush. That last group is estimates, not Google's numbers. Start with Search Console, it's free and it's the only one that's real data from Google.