unlawful detainer - wederrechtelijke onthouding

http://www.barthokriek.nl/ondertiteling/lijsten/juridisch/d....

Detainer - seems to be an act rather than a person or entity:

The act (or the juridical fact) of withholding from a lawfully entitled person the possession of land or goods, or the restraint of a person's personal liberty against his or her will; detention. The wrongful keeping of a person's goods is called an Unlawful Detainer although the original taking may have been lawful.

https://en.wikipedia.org/wiki/Detainer

A Forcible Entry and Detainer is an action that a landlord, or new property owner can take if the existing occupant refuses to leave after appropriate notice. This occupant could be either a tenant or original owner of property that was sold at a foreclosure or trustee's sale. The laws governing forcible entry and detainer actions are different if the property is residential or non-residential.
http://definitions.uslegal.com/f/forcible-entry-and-detainer...

Courts commonly refer to eviction actions as "forcible entry and detainer" or "unlawful detainer" actions. The legal theory is that the landlord alleges the tenant unlawfully continues to have use and possession of the rental property, and the landlord seeks the assistance of the court to have the tenant removed.
http://realestate.findlaw.com/landlord-tenant-law/eviction-a...

Eviction is the removal of a tenant from rental property by the landlord. In some jurisdictions it may also involve the removal of persons from premises that were foreclosed by a mortgagee (often, the prior owners who defaulted on a mortgage).

Depending on the laws of the jurisdiction, eviction may also be known as unlawful detainer, summary possession, summary dispossess, summary process, forcible detainer, ejectment, and repossession, among other terms. Nevertheless, the term eviction is the most commonly used in communications between the landlord and tenant.
https://en.wikipedia.org/wiki/Eviction