An Authoritative DNS server holds the information for the domain (e.g. dnsfilter.com) it serves.
An authoritative nameserver is responsible for providing recursive DNS servers with the IP address and other information about the domain being queried.
This information can be contained in an A record or a CNAME record if the domain has an alias.
Authoritative DNS servers are not always part of a DNS query, this is because the information they provide is sometimes cached by recursive DNS servers and DNS clients the first time it is received. If a user attempts to access a domain they already have, and the authoritative DNS information is cached, the query will resolve without contacting the Authoritative Name servers.
An authoritative nameserver is the last point of call in a DNS query operation when the DNS client makes a (does not go through its cache) fresh request for the domain’s IP address.
As shown in the diagram, a DNS query goes through a tree-like path from root servers through recursive servers to finally find the information for the domain on the server that is authoritative for that domain.