A person in a capitalist society who is forced to sell themselves, their time and their labor out on the labor market and whose life, therefore, is not entirely their own, is suffering under wage slavery.

This person is known as a wage slave.

Some people take offense when this phrase is used. "Slavery" is usually defined as a condition where an individual is compelled by force to work without sufficient monetary and/or material compensation. Since "wage slaves" are not under the threat of a master's whip, and since they supposedly have "choices", they are not (say those offended) slaves.

To understand why a wage laborer is a slave, one must first understand that the capitalist system itself is a form of whip, held by the wealthy capitalist/owner/boss; the slavemaster. As the mass of people are denied democratic access to resources, means of production and means of distribution, they are beholden to those who have managed (through force, be it physical, political or economic) to aggrandize and monopolize all of the above.

As such, you, the wage slave, must labor for the master and, in return, be paid a small fraction of what your work is worth to the master. You must do this simply to survive.

The master can use your position as wage slave to force you to work long hours, in bad condidtions, and to place "work" above "living". If you refuse to wholly submit, the master can fire you. This is known as a "flexible labor market".

There are two ways out of the wage slavery system as it currently stands.
1. Amass wealth; become a master. Live off the interest on your large bank account and/or savings. Then do only the work you enjoy and you find fulfilling, at the expense of all the other wage slaves who've made your situation possible.
2. Drop out. Become a subsistance farmer and/or subsistance hunter.

There is a third way, of course; the creation of an entirely different economic and political system based on democratic self management of workers and consumers, access to resources, and community control of the means of production and distribution. This is called Participatory Economics.