Tranquillity (also spelled tranquility) is the quality or state of being tranquil; that is, calm, serene, and worry-free. The word tranquillity appears in numerous texts ranging from the religious writings of Buddhism—where the term passaddhi refers to tranquillity of the body, thoughts, and consciousness on the path to enlightenment—to an assortment of policy and planning guidance documents, where interpretation of the word is typically linked to engagement with the natural environment. It is also famously used in the Preamble to the United States Constitution, which describes one of the purposes for which the document was establishing the government as to "insure domestic Tranquility".