A more thorough explanation:

An unlawful detainer, also known as an eviction lawsuit, is a legal process to determine who has the right to possess a property. The only issue that can be decided in an unlawful detainer case is who has the right to possess the property, and no other issues can be decided without the agreement of all parties involved.

For a landlord to pursue an unlawful detainer, they must show that they followed the proper procedures, such as giving the tenant a written notice to pay rent or leave the property. To win an unlawful detainer case for nonpayment of rent, the landlord must prove that the tenant is in possession of the property without permission, is behind on rent payments, and was properly served with a written notice to pay rent or leave the property. If the tenant does not pay the rent or leave the property within three days of receiving the notice, the landlord can file an unlawful detainer lawsuit.

However, an unlawful detainer case can also be filed for other reasons, such as if the tenant is damaging the property or using it illegally. For example, if a tenant is renting out a property on Airbnb without the landlord's permission, the landlord can file an unlawful detainer lawsuit to regain possession of the property.

If the landlord wins the unlawful detainer case, they are entitled to remedies such as possession of the property and any unpaid rent. In some states, landlords can also file a "rent and possession action" against a tenant.

Overall, an unlawful detainer is a legal process that landlords can use to regain possession of their property when a tenant is not following the terms of their lease agreement.