How to add explanation of terms in equation

Question

How can I add explanation like that in figure in LateX under my equation?

Answer 1

Something like this?

\documentclass{article}
\usepackage{amsmath} % for "align*" environment
\begin{document}
\[ \text{(main equation here)} \]
\begin{align*}
\text{where:}\quad 
K &= \text{conveyance for subdivision}\\
n &= \text{Manning's roughness coefficient for subdivision}\\
A &= \text{flow area for subdivision}\\
R &= \text{hydraulic radius for subdivision (area\slash wetted perimeter)}
\end{align*}
\end{document}

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Addendum: If the text to the right of the = symbols can be quite lengthy, you may get line overflows. If that's the case, you could use \parbox[t]{5cm}{...} instead of \text{...} instructions, where 5cm is a stand-in of the width of the text boxes you want. I recommend setting the material in narrow-width text boxes \RaggedRight rather than fully justified (which is the default); the latter can generate large interword gaps if the text box is narrow.

\documentclass{article}
\usepackage{amsmath}  % for "align*" environment
\usepackage{ragged2e} % for "\RaggedRight" macro
\begin{document}
\[ \text{(main equation here)} \]
\begin{align*}
\text{where:}\quad 
K &= \text{conveyance for subdivision}\\
n &= \parbox[t]{5cm}{\RaggedRight Manning's roughness coefficient for subdivision}\\
A &= \text{flow area for subdivision}\\
R &= \parbox[t]{5cm}{\RaggedRight hydraulic radius for subdivision (area\slash wetted perimeter)}
\end{align*}
\end{document}