I am slightly confused between DNS and Name server. Are they the same thing or is there a difference between two?
There is no such thing as a Domain Name Server.
DNS stands for Domain Name System, which is simply a hierarchy of Name Servers that has the intent to translate host names into IP addresses on a global scale. A name server hosts or caches these translations, in the case where they are hosted the name server is often called a DNS Server.
Counting all name servers is a bit tricky, because you can't simply enumerate all the domains.
Let me give you an example on resolving
The term name servers are also used in different contexts, read Spiff's answer for more.
A DNS Server typically is for converting FQDN (www.xxx.com) to IP Addresses (192.168.0.1).
(A DNS Server also does a lot more, it can perform reverse lookups, and in recent years does a lot of other tasks with text tags, geo-ip and a lot more).
On the other hand, a Name Server typically is a DNS Server, however, the name "Name Server" is typically used to locate a DNS Server.
For example, On a Whois record, a Name Server is typically the address for the DNS server that hosts the records for that domain.
As for how many are there - how long is a piece of string! This is an impossible question to answer... As a guess, I would put it in to the hundreds of thousands, if not low millions (for publicly accessible DNS Servers).
In some contexts, the term "name server" can refer to servers that aren't part of the Internet Domain Name System. For example, a WINS server is a name server for Microsoft's legacy proprietary networking protocols. There may have been other legacy LAN systems that had their own types of name servers that weren't part of Internet DNS.
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The acronym DNS means Domain Name System. It is a distributed system for translating host names (and other data) to IP addresses in a large scale (world). The
There are many name servers, but you don't need to know how many since they are queried as needed. There are only a few "root" name servers (the DNS is hierarchical).