\begin{definition}[Definition:Hybrid Mechanistic and Empirical Model]
Let $P$ be a real-world phenomenon of which we have incomplete theoretical knowledge.
Hence it cannot be modelled entirely using a mechanistic model.
However, our incomplete theoretical knowledge may suggest that a suitable class of mathematical functions can be used, which can then be fitted empirically.
Thus, the values of the parameters and the number of terms of the stochastic process being modelled need to be determined.
Such a model is referred to as an '''hybrid mechanistic and empirical model'''.
\end{definition}