All-taxa biodiversity inventory

An all-taxa biodiversity inventory, or ATBI, is an attempt to document and identify all biological species living in some defined area, usually a park, reserve, or research area. The first use of the term appears to have been in 1993, in connection with an effort initiated by ecologist Daniel Janzen to document the diversity of the Guanacaste National Park in Costa Rica. 
One of the most active and perhaps most thorough ATBIs to date focuses on the Great Smoky Mountains National Park of the southeastern United States. Initiated in 1998, the Smokies ATBI is managed by a non-profit NGO, called Discover Life in America, in coordination with the National Park Service. Over more than 20 years, the Smokies ATBI has added more than 10,000 species records for Great Smoky Mountains National Park, including more than 1,000 newly-described species, bringing the total known diversity of the Park to over 20,000 species.
A study assessed the species richness of a mega-diverse order of insects as a result of Zurquí All Diptera Biodiversity Inventory project at Costa Rica for one year, identifying more than 40,000 flies to 4,332 species, including 73 of the world's 160 Diptera families.
A number of other, similar, efforts have been initiated for a variety of parks and research field stations.
All ATBIs are inherently incomplete since, a) the biota of even well-studied areas includes many undescribed and often difficult-to-study species, and b) new species are regularly established through immigration and introduction.