According to the announcement from Ancestry.com:
This database details those persons enumerated in the Slave Schedule of the 1850 United States Federal Census, the Seventh Census of the United States. Slaves were enumerated separately during the 1850 and 1860 censuses, though, unfortunately, most schedules do not provide personal names. In most cases, individuals were not named and only details such as age, sex, and color are recorded. However, some enumerators did list the given names of slaves, particularly those over one hundred years of age. These names are generally found in the “name of slave owners” column. The names of owners are recorded. Other questions asked about the slave include whether a fugitive from the state (meaning if the slave had fled and not returned); number manumitted (or freed); and whether deaf and dumb, blind, insane, or idiotic.
Sometimes the listings for large slaveholdings appear to take the form of family groupings, but in most cases slaves are listed from eldest to youngest with no apparent effort to portray family structure. In any event, the slave schedules themselves almost never provide conclusive evidence for the presence of a specific slave in the household or plantation of a particular slaveholder. At best, a census slave schedule can provide supporting evidence for a hypothesis derived from other sources.
The slave schedule is especially useful for researchers who are seeking information about their slaveholding ancestors. This is because of the specific information it provides about their holdings and other information you can draw from it. For example, the number of slaves enumerated under an owner could help you determine if he had a plantation or not, and if so, what size it was.
The slave schedule was used in the following states: Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, Missouri, New Jersey, North Carolina, South Carolina, Tennessee, Texas, Virginia.
The United States was the first country to call for a regularly held census. The Constitution required that a census of all “Persons…excluding Indians not taxed” be performed to determine the collection of taxes and the appropriation of seats in the House of Representatives. The first nine censuses from 1790 to 1870 were organized under the United States Federal Court system. Each district was assigned a U.S. marshal who hired other marshals to administer the census. Governors were responsible for enumeration in territories.
The official enumeration day of the 1850 census was 1 June 1850. All questions asked were supposed to refer to that date. By 1850, there were a total of thirty-one states in the Union, with Florida, Texas, Iowa, Wisconsin, and California being the latest editions. There were no substantial state- or district-wide losses.
Taken from Szucs, Loretto Dennis, “Research in Census Records.” In The Source: A Guidebook of American Genealogy, ed. Loretto Dennis Szucs and Sandra Hargreaves Luebking (Salt Lake City: Ancestry, 1997).
William Dollarhide, The Census Book: A Genealogist’s Guide to Federal Census Facts, Schedules and Indexes, Heritage Quest: Bountiful, Utah, 2000.
The 1850 U.S. Federal Census Slave Schedules may be found at https://www.ancestry.com/search/collections/1850slaveschedules/.