Wrapped Bitcoin, or WBTC, is a token that represents BTC 1:1 on the Ethereum network. By representing BTC on Ethereum, it can be included in DeFi applications, including AirSwap. It is governed by a DAO, which AirSwap is a part of. Custody of WBTC is maintained by BitGo, a regulated custodian.
To learn more about wBTC, head over to the official wBTC website.