What's in a name? That which we call a rose By any other name would smell as sweet
A rose (or any other "thing") doesn't have a built-in identifier. "Rose" is just the name we (English-speaking) humans use to identify the the actual thing. If we all agreed to call them "pflegnarches" (silent p) it wouldn't change the nature or identity of the underlying thing.
Shakespeare aside, this concept applies to things, people, domain names, emails, phone numbers, etc. Even if you didn't know me as "Luke" from "thekoinpress.com", I'd still be here writing and podcasting about blockchain accessibility.
Domain names in particular are unique. Since I own "thekoinpress.com" no one else can. There's lots of other Lukes, so it's useful to have a domain. My domain and so many others belong to the .com "top-level domain" or TLD. These TLDs are managed by an organization called ICANN, and it's very expensive and time consuming to create new TLDs (if they let you do it at all). Today, you can get a domain name under .com, .io, .xyz, .link, and a bunch of others.
The first top-level domain to really break away from ICANN is .eth -- the Ethereum Name Service TLD.
On Ethereum, you can lease an NFT for ~$5/year (more for short domain names) and have a blockchain-powered domain name. Unfortunately, because .eth isn't supported by ICANN, you can't just type "yourname.eth" into any browser and expect a website to show up. You need a browser (or browser extension) that supports .eth domains. Or you can use a proxy website like eth.limo or eth.link.
Sounds like a hassle, right? So what's the point?
Storing domain names on-chain allows you to securely identify users and dApps are the real deal. It's easier to remember someone's name than it is to copy a 32 character address. These names don't change the identity of who owns the address. It just makes it easier to identify them securely.
P.S. I'm brewing up a Koinos equivalent to ENS, so if you want to know more, ask away!