A DNS server is a computer server that contains a database of public IP addresses and their associated hostnames, and in most cases, serves to resolve, or translate, those common names to IP addresses as requested.
DNS servers run special software and communicate with each other using special protocols.
In more easy to understand terms: a DNS server on the internet is the device that translates that www.stubcreator.com you type in your browser to the 146.66.110.159 IP address that it really is.
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