A stylized calligraphic script font variant commonly used for denoting mathematical categories, operators, or special sets.
Examples
Script font for mathematical operators or special sets
\mathscr{L} \text{ is the Laplace transform operator}
Script font in functional analysis
\mathscr{H} \text{ denotes a Hilbert space}
Script font for algebras and categories
\text{Let } \mathscr{C} \text{ be a category and } \mathscr{F}: \mathscr{C} \to \mathscr{D} \text{ be a functor}