Why doesn't the IEEEtran document class recognize “definition” environments?

Question

I have an IEEEtran document class. I want to put a simple definition inside the document:

\begin{definition}
blab bla
\end{definition}

I am getting the error below:

Environment definition undefined. \begin{definition}

Answer 1

IEEEtran defines its own environments which is used to replace existing ones (like enumerate, itemize, etc.). However, it doesn't define any definition environment. You can do so by using \newtheorem:

\documentclass{IEEEtran}% http://www.ctan.org/pkg/ieeetran
\newtheorem{definition}{Definition}
\begin{document}
\begin{definition}
Here is a definition.
\end{definition}
\end{document}​