Definition of classes:
(n) :
(countable) A group, collection, category or set sharing characteristics or attributes.
(n) :
(sociology, countable) A social grouping, based on job, wealth, etc. In Britain, society is commonly split into three main classes: upper class, middle class and working class.
(n) :
(uncountable) The division of society into classes.
(n) :
(education, countable and uncountable) A group of students in a regularly scheduled meeting with a teacher.
(n) :
A series of lessons covering a single subject.
(n) :
A single lesson in a series.