DNS, or the Domain Name System, is a system that maps human-friendly domain names to IP addresses, which are unique numerical identifiers that are used to locate servers and devices on the Internet. In other words, DNS is like a phonebook for the Internet, translating easy-to-remember domain names, such as "google.com" or "facebook.com", into the IP addresses that computers use to communicate with each other.
When you type a domain name into your web browser or click on a link, your computer sends a request to a DNS server, asking it to translate the domain name into an IP address. The DNS server looks up the IP address in its database and returns it to your computer, which then uses the IP address to connect to the server that hosts the website or service you are trying to access.
DNS is an essential component of the Internet, enabling millions of people to access resources on the web using easy-to-remember domain names, rather than having to remember the IP addresses of every website they want to visit. Without DNS, the Internet would be much more difficult to use and navigate.