A set, collection, group, or configuration containing members regarded as having certain attributes or traits in common; a kind or category. A division based on quality, rank, or grade, as: A grade of mail: a package sent third class. A quality of accommodation on public transport: tourist class. A social stratum whose members share certain economic, social, or cultural characteristics: the lower-income classes. Social rank or caste, especially high rank. Informal Elegance of style, taste, and manner: an actor with class. A level of academic development, as in an elementary or secondary school. A group of students who are taught together because they have roughly the same level of academic development. A group of students or alumni who have the same year of graduation. A group of students who meet at a regularly scheduled time to study the same subject. The period during which such a group meets: had to stay after class. Biology A taxonomic category ranking below a phylum or division and above an order. See Table at taxonomy. Statistics An interval in a frequency distribution. Linguistics A group of words belonging to the same grammatical category that share a particular set of morphological properties, such as a set of inflections. To arrange, group, or rate according to qualities or characteristics; assign to a class; classify.