In simple terms, if your website was a house, then your domain name will be its address.
A more detailed explanation:
The Internet is a giant network of computers connected to each other through a global network of cables. Each computer on this network can communicate with other computers.
To identify them, each computer is assigned an IP address. It is a series of numbers that identify a particular computer on the internet. A typical IP address looks like this:
Now an IP address like this is quite difficult to remember. Imagine if you had to use such numbers to visit your favorite websites.
Domain names were invented to solve this problem.
Now if you want to visit a website, then you don’t need to enter a long string of numbers. Instead, you can visit it by typing an easy to remember domain name in your browser’s address bar.