The Domain Name System (DNS) is a distributed database in which you can map hostnames to IP addresses through the DNS protocol from a DNS server. Each unique IP address can have an associated hostname.
If it's not a system, the term 'DNS server' becomes mysterious.
On a side note, I misread IoT as LOT at one point and selfishly believed it to be an acronym for 'Life of Technology'. Confirmation of abbreviations is important.