\begin{definition}[Definition:Formal Semantics/Structure]
Let $\LL$ be a formal language.
Part of specifying a formal semantics $\mathscr M$ for $\LL$ is to specify '''structures''' $\MM$ for $\mathscr M$.
A '''structure''' can in principle be any object one can think of.
However, to get a useful formal semantics, the '''structures''' should support a meaningful definition of validity for the WFFs of $\LL$.
It is common that '''structures''' are sets, often endowed with a number of relations or functions.
\end{definition}