As Brent.Longborough mentioned in his comment, one option would be to use the nomencl package. Another option (allowing you to have not only the symbols and their descriptions, but also the page(s) in which they occur (typically one would use the page in which the concept is defined)) would be to use the glossaries package; a little example:
\documentclass[a4paper]{memoir}
\usepackage[style=super]{glossaries}
\makeglossaries
\renewcommand\glossaryname{List of Symbols}
\newglossaryentry{Cab}{name={$C[a,b]$},
sort=C,
description={The space of continuous functions defined on $[a,b]$}
}
\newglossaryentry{C1ab}{name={$C^{1}[a,b]$},
sort=C,
description={The space of differentiable functions with continuous derivatives defined on $[a,b]$},
}
\begin{document}
Next, we introduce The space \gls{Cab} of continuous functions defined on $[a,b]$ and its subspace \gls{C1ab} of differentiable functions with continuous derivatives defined on $[a,b]$.
\printglossaries
\end{document}
an image of the first page of the resulting document:

and an image of the resulting "List of Terms":

The glossaries package offers you many customization possibilities; please refer to the package documentation.
nomenclpackage might be what you need. – Brent.Longborough Mar 07 '13 at 21:13memoirclass -- given that one includes in the source.texfile the commands\makeglossaryand\printglossaryalong with syntactically correct\glossaryentries? – murray Jul 30 '16 at 01:08