still another possibility, using tabbing. this has the advantage that it
can break across pages, anywhere in the list.
it's necessary to determine which left-hand entry is longest, to set the
width of the left column for the \kill line, but that needs to be done only once,
and is easy to change if a new, wider entry is added.
\documentclass{article}
\newcommand{\hyline}[2]{%
$#1$\> --\kern.5em #2 \\}
\begin{document}
\begin{tabbing}
$S_m(b)$ \ \= \kill
\hyline{I(b)}{interrogating signal}
\hyline{h_n}{forward ross}
\hyline{h_f}{reversequite}
\hyline{h}{product of all and wox}
\hyline{F_h(t)}{interrrr}
\hyline{S_m(b)}{m\textsuperscript{th} reponse of $x$ thererer}
\hyline{b(t)}{received signal}
\hyline{\omega(x)}{noise added $\omega$ read}
\end{tabbing}
\end{document}

if a right-hand-side entry appear that is longer than the page width will allow,
the #2 in the definition of \hyline (a shorter command name could be used,
of course), a \parbox of appropriate size could be applied, with its contents
set ragged right. this would ensure that appropriate baselines are used within
a single entry, a benefit if you decide that a little extra space should be
applied between entries (presumably as an optional dimension inserted after the
\\[...] in the definition).
tabbing? it isn't that much different fromtabular, and it has the advantage that it can break across pages. – barbara beeton Dec 02 '14 at 13:17