A recursive DNS server is one that performs the full lookup process for a domain. When a user queries a domain name, the recursive server will search through various DNS servers to resolve the query, starting from the root and working its way down to find the correct IP address. In contrast, an authoritative DNS server only provides answers for domains it is directly responsible for.
A recursive lookup is when a DNS resolver takes a client’s query and does the work of walking the hierarchy (root → TLD → authoritative) until it gets a final answer, then caches it. They are done by recursive resolvers run by ISPs, enterprises, and public providers (e.g., Google Public DNS 8.8.8.8, Cloudflare 1.1.1.1, Quad9) or by software like Unbound, BIND in recursive mode, Knot Resolver, and PowerDNS Recursor. Authoritative servers do not perform recursion.