Trespassing is the act of entering land or property owned by another without permission or other lawful reason to be there. One who commits this crime is known as a trespasser.
In 2366, Jean-Luc Picard termed the illegal colonists on the Sheliak world Tau Cygna V trespassers, as they were there in violation of the Treaty of Armens. (TNG: "The Ensigns of Command")
As of that same year the Sarthongians, according to Picard, were known for treating trespassers harshly. He informed Vash of this upon learning she wished to travel to the ruins of Sarthong V for an archaeology expedition. She did travel there and told Picard the following year that she obtained several impressive artifacts from the planet. (TNG: "Captain's Holiday", "Qpid")