Domain name system (DNS): A global and highly distributed network service that resolves strings of letters into IP addresses for you

Domain name: the term we use for something that can be resolved by DNS

ex.

www.weather.com → mapped to ip addresses

and the corresponding mapped ip address could change due to variety of reasons.

ex.

www.weather.com is moving their data centre from one place to another. By changing the resolved ip address for the domain name www.weather.com, end users would notice any difference in service.

Not only does DNS make it easier for humans to remember how to get to a website, it also lets administrative changes happen behind the scenes without an end-user having to change their behavior.

Even though datas travel through cables at speed of light it’s going to be quicker to transmit a certain amount of data between places that are geographically close to each other.

Instead of keeping all your web servers in on eplace, you could distribute them across data centers across the globe. (A cache server)

DNS helps provide this functionality. DNS let’s organizations decide if you’re in the region, resolve the domain name to this IP. If you’re in this other region, resolve this domain to this other IP.