The total value of ETH and BTC locked up in contracts as collateral for defi-products.
It is mainly ETH, small amount of BTC. ETH that is locked up reduces supply, thereby possibly creating upwards pressure on the price. However, it is likely that people who lock ETH up for defi are long term hodlers anyway, which should dampen the effect.
EDIT: the amount of ETH locked up is currently ~ 2.17 million: https://defipulse.com/