parasite single
A wasei-eigo term for an unmarried adult who lives with their parents and relies on them for housing and often other support, despite having a sufficient income to live independently. Often carries a mildly critical or sociological tone.
wasei-eigo (Japanese-coined English), from parasite single
It is said that the number of parasite singles has been increasing recently.
He is a parasite single who still lives with his parents even though he's over 30.