The proletariat is not the lowest social class. This role is befallen to the Lumpenproletariat.

Proletariat corresponds to the "working poor" class, and is seen as the only true revolutionary class. The lumpenproletariat is not even a real social class : it is composed of people who live on the fringe of society, the ones for whom surviving is a daily challenge. They are highly despised by Marx, who saw no revolutionary potential in them.