Wage slavery is a term used to refer to the situation in which people are extremely dependent on their wages and jobs and that it creates a situation that resembles to that of owning that person, hence to slavery. It is used to refers to situations in which labor means exploitation.
In the 19th century there was a decline in the use of this word and substituted by "wage work", specially due to the Industrial Revolution, the dominance of the manufacturing activities and the irruption of the trade union system. This change of terms was the way of perpetuating it under a different denomination, but continuing the same practice.