\documentclass[12pt]{article}

\begin{document}

\section*{Description environment}
Only for demonstration all Labels are boxed.
\subsection*{Bottom aligned label}

previous paragraph with some nonsense text for the demonstration of list environments.

\begin{description}
\item [\fbox{{\parbox[b]{.5\linewidth}{This is a very long and over more than one
line long, a so called multiline label}}}]
	and now comes some text for this description environment, which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long than the forgoing line from the
multiline example.
\end{description}


\begin{verbatim}
\begin{description}
\item [\fbox{{\parbox[b]{.5\linewidth}{This is a very long and 
  over more than one line long, a so called multiline label}}}]
  and now comes some text for this description environment, 
  which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long 
  than the forgoing line from the multiline example.
\end{description}
\end{verbatim}


Next paragraph with some nonsense text for the demonstration of list environments.

\subsection*{Top aligned label}
\begin{description}
\item [\fbox{{\parbox[t]{.5\linewidth}{This is a very long and over more than one
line long, a so called multiline label}}}]
	and now comes some text for this description environment, which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long than the forgoing line from the
multiline example.
\end{description}

\begin{verbatim}
\item [\fbox{{\parbox[t]{.5\linewidth}{This is a very long and over more than one
line long, a so called multiline label}}}]
	and now comes some text for this description environment, which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long than the forgoing line from the
multiline example.
\end{verbatim}

Next paragraph with some nonsense text for the demonstration of list environments.

\subsection*{Centerd label}
\begin{description}
\item [\fbox{{\parbox{.5\linewidth}{This is a very long and over more than one
line long, a so called multiline label}}}]
	and now comes some text for this description environment, which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long than the forgoing line from the
multiline example.
\end{description}

\begin{verbatim}
\begin{description}
\item [\fbox{{\parbox{.5\linewidth}{This is a very long and over more than one
line long, a so called multiline label}}}]
	and now comes some text for this description environment, which is still nonsense, too.
\item [\fbox{Next}] This is again a line, but not so long than the forgoing line from the
multiline example.
\end{description}
\end{verbatim}

Next paragraph with some nonsense text for the demonstration of list environments.

\end{document}