The speed prior is a complexity measure similar to Kolmogorov complexity, except that it is based on computation speed as well as program length. The speed prior complexity of a program is its size in bits plus the logarithm of the maximum time we are willing to run it to get a prediction.
When compared to traditional measures, use of the Speed Prior has the disadvantage of leading to less optimal predictions, and the advantage of providing computable predictions.
References
Speed prior Wikipedia(Text) CC BY-SA