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

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}

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 The class defines no theorem-like environment. Use \newtheorem. – egreg Jun 26 '12 at 15:14

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