unlawful detainer n1 : the act of wrongfully remaining in possession of property (as after expiration of a lease)
2 : an action intended to remedy unlawful detainer by restoring possession of property to its owner called also unlawful detainer action
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.