This term was first used by Masahiro Yamada of Tokyo Gakugei University in his book The Age of Parasite Singles. A parasite is basically an organism that feeds off another organism, but contributes nothing to the host. In Yamada’s book he talks about how modern Japanese parents are the host and their offspring are parasites.
Since the 1970s this phenomenon has being steadily increasing. It is now said that in Japan, approximately 60% of men and 80% of women between 20-34 live with their parents. 85% do not help with the living expenses and 50% receive additional financial aid from their parents. Source
I’ve noticed a lot of parasite singles stay with their parents until they marry. Some say they stay with their parents because it’s too expensive to live independently. However, I don’t think it’s an economical problem since many young professionals could afford to live on their own (depending on their lifestyle choices).
Overall, I think living on your own (or at least with another group of people, e.g., apartment sharing) should be encouraged because you develop new skills and learn to adapt to new situations. This kind of experience and the life skills you develop are like a rite of passage into adulthood.
Living with your parents is not really the problem though. The problem is being parasitic. If you’re living with your parents, you should contribute something. Unfortunately, it’s very easy to have a parasitic relationship if you’re living with your parents as an adult, because for more people, other than replacing school with work, not much seems to change.