\begin{definition}[Definition:Boundary Condition]
Let $\Phi$ be a differential equation to which a particular solution is to be found.
A '''boundary condition''' is an equation relating particular values of the dependent and independent variables which the particular solution to $\Phi$ must satisfy.
It is usual for such '''boundary conditions''' to correspond to the physical extremities of bodies, aspects of whose internal nature is being modelled by means of $\Phi$.
\end{definition}