When a DNS query takes place, the information can be directly from the authoritative server or from a server that has been provided from elsewhere. The latter servers are referred to as non-authoritative servers. As a general rule of thumb, the authoritative server will be a DNS server belonging to the domain itself. A non-authoritative server will be one that holds a copy of some or all of the information that's held by the authoritative server. For example, a lot of organizations have Google's public DNS server at 8.8.8.8 specified as one of the servers to perform DNS queries against. Any queries this server responds to would be classed as non-authoritative.
A basic DNS server will be broken down into a forward lookup zone, ...
