Refers to the calligraphic {math-mode} font accessed via \mathcal.
Refers to the calligraphic math-mode font accessed via \mathcal. The default font representation looks like this:
\documentclass{article}
\pagestyle{empty}
\begin{document}
$\mathcal{A\ B\ C\ D\ E\ F\ G\ H\ J\ K\ L\ M\ N\ O\ P\ Q\ R\ S\ T\ U\ V\ W\ X\ Y\ Z}$
\end{document}
Although, other representations of \mathcal also exist (see Comprehensive LaTeX Symbol List, Table 213):
