The term Classical Ballet has a couple meanings.  It can be used to describe a style as well as a type of ballet.

As a style of ballet, the term classical ballet is used to describe the traditional style of ballet, which features the academic technique developed and taught over the centuries.

As a type of ballet, a classical ballet is a ballet with the style and structure of the typically used framework established in the nineteenth century.  For example, classical ballets are Swan Lake, Giselle, The Nutcracker, Coppélia, The Sleeping Beauty, among many more.  Basically, most “story ballets” are considered classical ballets. An example of a ballet that is not classical, rather an abstract ballet or contemporary ballet, could be William Forsythe’s “In the Middle, Somewhat Elevated.”