The working class is usually thought of as the lowest social class of people in societies that care about class structure. Often, they are labeled "lower class" to reflect this, the others being the comfortable middle class and the upper class.
Another term for the working class, used often in socialist literature, is "proletariat." The term, derived from the Latin word for "wage earner," was given its current definition by Marx, and it refers to people that are owners of labor power, but have no other capital to speak of. It also can be used as a generic term for the lowest class in a given community.
Followers of the various derivatives of Marxism will often describe the working class as the second lowest class, the real lowest being a "benefits class" or "underclass", which comprises the poor that other classes don't feel empathy for. Marx described this class as the "lumpenproletariat" or "rogue proletarians," comprising such people as beggars, con-men, and others who were the most unlikely to come to the gospel light of class consciousness, and thus completely useless for revolutionary purposes. Later theorists disagreed on this point; thinking that some use might be got out of the lumpenproletarians after all, they have included among their number the permanently unemployable and those who lost the Skin Color Lottery.