A parbox is a box whose contents are created in paragraph mode. The
\parbox has two mandatory arguments:
width: specifies the width of the parbox, and
text: the text that goes inside the parbox.
LaTeX will position a parbox so its center lines up with the center of
the text line. An optional first argument allows you to
line up either the top or bottom line in the parbox, by using as optional
position argument t or b, respectively .
A \parbox command is used for a parbox containing a small piece of
text, with nothing fancy inside. In particular, you shouldn't use any
of the paragraph-making environments inside a \parbox argument. For
larger pieces of text, including ones containing a paragraph-making
environment, you should use a minipage environment.