The phrase "parent basement" refers to when someone, often a young adult, still lives with their parents and resides in the basement of their house. Full definition
I will forget work, have no life, live in parents basement again... Doh too late. (toucharcade.com)
You insist that their is something and until you produce this something you are simply a troll sitting in your parents basement until your McDonald's shift starts. (religion.blogs.cnn.com)
So, now I sit all day long on my parents basement having fun being a moron to other people, eating cheese puffs and drinking mountain dew. (religion.blogs.cnn.com)