In normale minipage examples allways textwidth would be used to determine width of minipage. But also the paperwidth could be used too.
example
\documentclass{article}
\begin{document}
\noindent
\begin{minipage}{0.5\textwidth}
\fbox{frame around dummy text and more}
\end{minipage}
\begin{minipage}{0.5\textwidth}
\fbox{second framed dummy text and more}
\end{minipage}
\begin{minipage}{0.5\paperwidth}
\fbox{frame around dummy text and more}
\end{minipage}
\begin{minipage}{0.5\paperwidth}
\fbox{second framed dummy text and more}
\end{minipage}
\begin{minipage}{\paperwidth}
\fbox{third framed dummy text and more dummy text to show how big is paperwidth instead of textwidth}
\end{minipage}
\end{document}
How it looks:
