I am using some terminal output as a figure in a report I am writing and need to change just the text within the figure to monospace.
\begin{figure}[ht]
%bunch of text here
\caption{Mass calculation program output}
\label{fig:calcMass}
\end{figure}
Take a look at the (usually built-in) listings package. A tutorial can be found here.
The package includes syntax highlighting (if you're using bash) and can read input from external files (which can be useful if you're documenting a program you're writing and don't want to manually change the LaTeX code if you make a change in the program).