What it is
Fetches the page and matches it against Wappalyzer's fingerprint set, a large collection of regular expressions that recognise the traces different technologies leave behind in markup, headers, script paths and cookie names.
Why it matters
Knowing the framework, CMS, analytics and payment provider narrows down which vulnerabilities are worth checking, and shows which third parties have a hand in serving the page. Detection is inference rather than certainty, and reported version numbers in particular are often wrong.