I would like to tell you first what is server? i think you know very well that Server is something which serves your requests. So anything which responses your requests, is called Servers.
If we talk about types of server then i think that is not sure we need to specify in which you define the types of server. Here you can see some servers which is actually categorized on the basis of their particular operation/responses.Example:
And many more...
DNS is actually Domain Name System which assign URL name for I.P Addresses. The Domain Name System makes it possible to assign domain names to groups of Internet resources and users in a meaningful way, it associates various informations with Domain Name. For Example,
Let a domain name www.example.com may be translated into the I.P address 18.104.22.168
"People says 143. I say 444 i.e. Love Your Life"