ENS stands for The Ethereum Name Service and it behaves very similar to how DNS behaves in the web2 space.
As we all know that Ethereum has long addresses which are hard to remember or type
ENS solves this issue by translating these wallet addresses, hashes etc into readable domains which are then saved on Ethereum blockchain
The best part about ENS is unlike DNS servers which are centralized, ENS works with the help of a smart contract which is censorship resistant.
So now when you are sending your wallet address to someone which looks like 0x1234huiahi.... you can actually send them tom.eth and the ENS would figure out that tom.eth is actually equal to your wallet address (0x1234huiahi....)