Text under equation
Just for fun (this may not be the optimal way of doing this):
\documentclass[12pt]{article}
\pagestyle{plain}
\usepackage[margin=1.8cm]{geometry}
\geometry{a4paper}
\usepackage[parfill]{parskip}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[usenames]{color}
\definecolor{cyan}{rgb}{0,1,1}
\newcommand{\cyan}[1]{\textcolor{cyan}{#1}}
\definecolor{black}{rgb}{0,0,0}
\newcommand{\black}[1]{\textcolor{black}{#1}}
\begin{document}
\[
\text{read stall cycles} =
\cyan{\underbrace{\black{\frac{\text{reads}}{\text{program}}
\times \parbox{48pt}{read miss \\ rate (\%)}}}_{\text{read
miss per program}}} \times
\cyan{\underbrace{\black{\parbox{76pt}{read miss \\ penalty
(cycle)}}}_{\parbox{62pt}{\scriptsize\centering number of cycles \\
per read miss}}}
\]
\end{document}