They have not improved the cleanliness or levels of sanitation. The term was coined by the Joint Monitoring Program (JMP) for Water Supply and Sanitation of UNICEF and WHO in 2002 to help monitor the progress towards Goal Number 7 of the Millennium Development Goals (MDGs). The opposite of "improved sanitation" has been termed "unimproved sanitation" in the JMP definitions.
The Joint Monitoring Program (JMP) for Water Supply and Sanitation has been publishing updates on the global sanitation situation on an annual basis. For example, in 2014, only 40 percent of the world's population had access to improved sanitation, as per the definition given below.
In 2017, JMP defined a new term: "basic sanitation service". This is defined as the use of improved sanitation facilities that are not shared with other households. A lower level of service is now called "limited sanitation service" which refers to use of improved sanitation facilities that are shared between two or more households. A higher level of service is called "safely managed sanitation". This is basic sanitation service where excreta are safely disposed of in situ or transported and treated offsite.
To allow for international comparability of estimates for monitoring the Millennium Development Goals (MDGs), the Joint Monitoring Program (JMP) for Water Supply and Sanitation defines "improved" sanitation as the following kind of toilets:
Sanitation facilities that are not considered as "improved" (also called "unimproved") are:
Whilst "shared" toilets are not counted as improved sanitation, data about usage of shared toilets is nevertheless report in the annual progress reports of the JMP.