The degree of coupling between assets is called "beta" - typically you're trying to reduce the coupling of one asset to another in your portfolio (explanation [1]) but you can definitely work the other way to make predictions.

I'm not sure what the technical term is for a time-lag correlation though, since that's what you're really after; it's not an interesting correlation for your model if you don't have time to trade ETH on the BTC signal.

[1]: https://www.quantopian.com/lectures/beta-hedging