What is DNS?

In mobile phones, we have phone books. If we need to save someone's phone number, how we do that? Do we just enter the number and save it? No, we attach the number to a person name or something we can remember. So, the next time we open the contact list, we can easily find it. In Boaz Yakin's film Safe, there was a little Chinese girl who could remember long numeric codes. But if I had such a memory, I have a lot of other things I would like to remember rather than a bunch of numbers. It is the same with when you are dealing with IP addresses. I remember a few of the most commonly used IP addresses in infrastructure. But I do not remember most others. I remember lots of servers by their hostnames rather than IP addresses. This is because hostnames are more user friendly and easy to remember than IP addresses. This is what exactly DNS does. It maps IP addresses...