What's a W-ETH?

This page would have saved me a few hours the first time I used a decentralized exchange, oasisdex.com, and I saw that all the tradings were done with W-ETH, not ETH, and I didn't know what was a W-ETH, and how I could get one.

TL;DR: in decentralized exchanges only tokens that comply with a specific standard (ERC20) can be traded. ETH doesn't, so you have to trade it for an ERC20 complaint token, W-ETH.