Both proletariat and bourgeoisie are terms commonly used in Marxist theory (and you are not terribly likely to encounter either one outside of that context).
The proletariat is the class of people in a society who work jobs that pay hourly and that usually involve physical work of some kind. Proletariat is often used interchangeably with working class.
The bourgeoisie is the class of people in a society that includes business and professional people, government officials, and highly skilled workers. Bourgeoisie is often used interchangeably with middle class.
