What does ehrenreich mean when she uses the term wage slave

Barbara Ehrenreich uses the term "wage slave" to describe
the situation in which many of her coworkers in the book find themselves. They are
employed and are being paid, so they can be called wage earners. However, the wages they
are receiving are so low that they cannot begin to cover the expenses involved in
living, such as paying for housing and food and work uniforms and health care. However,
the workers frequently have no alternative but to continue working for the inadequate
wages they are receiving because they have no transportation to a better work location,
no training to take a better-paying job, or no energy to undertake the process of
searching for alternative employment. In that sense, the workers are slaves to the
situations in which they are trapped.