The UN define "improved sanitation" as having access to adequate excreta disposal facilities, such as a connection to a sewer or septic tank system, a pour-flush latrine, a simple pit latrine or a ventilated improved pit latrine. An excreta disposal system is adequate if it is private or shared (but not public) and if it can effectively prevent human, animal and insect contact with excreta.

Source: UN Human Development Report 2006