\begin{definition}[Definition:Differential Equation/Solution]
Let $\Phi$ be a differential equation defined on a domain $D$.
Let $\phi$ be a function which satisfies $\Phi$ on the whole of $D$.
Then $\phi$ is known as '''a solution''' of $\Phi$.
Note that, in general, there may be more than one '''solution''' to a given differential equation.
On the other hand, there may be none at all.
\end{definition}