Difference between ETH and WETH?

WETH follows what is known as the ERC-20 standard, while ETH does not. WETH was created because ETH was not feasible to be used for various DeFi applications.
Thus, wrapping the ETH token in an ERC-20 compatible standard meant that it could easily be used across the wide spectrum of dApps. Also, this means that users can create their own versions of tokens for their custom DeFi applications.
Now, in the case of WETH, it is equivalent to ETH. This means that there is no price difference between ETH and WETH. Thus, if you wish to use your ETH to participate on a custom dApp, you can easily convert it into WETH on a dApp, like 1inch, and then continue using it.
Remember that ERC-20 is a technical standard for issuing tokens on the Ethereum blockchain. It only dictates the properties of the token. One of the most crucial aspects of an ERC-20 token is that it is fungible, which means that one token will always be exchangeable for another one of the same value.