\the-commandsWhenever you request a new LaTeX counter, LaTeX creates a bunch of behind-the-scenes commands, as well as definining the counter itself.
Among other things, \newcounter{fred} creates a command
\thefred, which expands to "the value of
fred" when you're typesetting.
The definition of \thefred should express the
value of the counter: it is almost always always a mistake to use the
command to produce anything else. The value may reasonably be
expressed as an arabic, a roman or a greek number, as an alphabetic
expression, or even as a sequence (or pattern of) symbols. If you
need a decision process on whether to re-define
\thefred, consider what might happen when you do
so.
So, for example, if you want your section numbers to be terminated by
a period, you could make \thesection expand with a terminating
period. However, such a change to \thesection makes the
definition of \thesubsection look distinctly odd: you are going to
find yourself redefining things left, right and centre. Rather, use
the standard techniques for
adjusting the presentation of section numbers.
Or, suppose you want the page number to appear at the bottom of each
page surrounded by dashes ("-- nnn --"). Would you want to
achieve this by redefining \thepage, given the likely appearance
of the table of contents with the dashes attached every page number,
or of the modified \pageref references. In this case, the
modification is best done by redefining the page style itself, perhaps
package fancyhdr.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=the-commands