In reply to MG: As I'm sure you know, it means people who sell their labour power to make a living as opposed to those who own the means of production, buy the labour power, add surplus value, and sell the product/service at a profit. Whether you agree that this happens in the way described, or think that there's anything wrong(or right) with that, is a different question, but this is what people who use the term to describe a section of society usually mean.