Composing the class of modern Capitalists, the bourgeoisie are the employers of wage laborers, and the owners of the means of production.
The means of production include not only the physical instruments of production (tools, machines, etc.), but also the methods of working (skills, forms of cooperation, division of labor, etc.), and knowledge that can be applied to production (science, etc.).
The economic structure of society that defines people's mode of living. It consists of the means of production as well as the relations of production.
The class of modern wage-laborers. They do not have their own means of production, and therefore they must sell their own labor in order to survive.
The necessary relations between people as required for a certain form of material production. The relations of production refer to the distribution of the means of production, the forms of possession (collective and individual private property), and the distribution of the product.