ENS Domains(Ethereum Name Service Domains) are a way to simplify wallet addresses. Wallet addresses are 64 characters long and can inhibit the sending of crypto. ENS uses domains to replace these wallet addresses. A good comparison is that of a nickname. Someone could have a very long name, so they are often referred to as a nickname for simplicity. This is how ENS works. It takes the long wallet address and consolidates it to a domain like alice.eth. These domains can be bought and sold. They require fees to be held.