The simple term for this is Sharpe Ratio https://en.wikipedia.org/wiki/Sharpe_ratio
If you want to get really deep into investment theory, Beta implies basically everything is a good investment in small enough amounts https://en.wikipedia.org/wiki/Beta_(finance)
Though in practice, Beta is mostly irrelevant beyond a relatively simple portfolio https://finance.yahoo.com/news/warren-buffett-myth-more-why-...