According to Wikipedia, adverse possession also known as "Sqautters' Rights" is defined as follows:
"In common law, adverse possession is the process by which title to another's real property is acquired without compensation, by holding the property in a manner that conflicts with the true owner's rights for a specified period. Circumstances of the adverse possession determine the type of title acquired by the disseisor (the one who obtains the title as a result of the adverse possession action), which may be fee simple title, mineral rights, or other interest in real property.
Adverse possession's origins are based both in statutory actions and in common law precepts, so the details concerning adverse possession actions vary by jurisdiction. The required period of uninterrupted possession is governed by the statute of limitations. Other elements of adverse possession are judicial constructs."