I have the following heat equation
Let $\Omega=\{(x,t) \;t\gt |x| \}$
and $u$ be a solution to the heat equation $$\begin{align} u_t -u_{xx}=0 &&(x,t)\in\Omega \\ u(x,t)=t &&(x,t) \in \partial \Omega \end{align}$$
The maximum principle states (in my script) that the maximum is obtained on the parabolic boundary. I am a little confused. What would be the parabolic boundary of $\Omega$ ?