The queried name server must either provide a response or return an error. Such clients issue a recursive query to the name server.
Recursive queries are like a request issued to a secretary.
Name servers often use this type of query between each other. As compared to the recursive queries, these queries do not require as much work. In an iterative query, the name server will return the best answer it knows or just point it to another name server to assist the resolution process of the querying name server. Based on other fields in a resource record, queries may request other arbitrary types of information for a domain. Such queries require an exhaustive search of the DNS database and are referred to as inverse queries.