Surrogate model
Beginner
A quick stand-in that guesses what a slow test would say, so you only run the slow test on the most promising options.
Novice
A cheap model fitted to the results of slow experiments, used to guess the result of experiments not yet run.
Expert
Gaussian processes, tree-based models and neural networks are common. A useful one reports how unsure it is along with its guess, which lets an optimizer balance trying unexplored settings against refining good ones.