Proxemics is the study of communicative aspects of space. Territoriality refers to personal space that individuals do not want others to invade. There are three types of territorial encroachments: invasion, violation, and contamination. Invasion involves taking over another's territory permanently. Violation is the unwarranted use of another's territory through sight, sound, or physical presence. Contamination is defiling another's territory through what is left behind rather than direct presence. Territorial defense uses prevention by marking space as one's own, and reaction such as standing one's ground when territory is challenged.