In the United States, the National Register of Historic Places classifies its listings by various types of architecture. Listed properties often are given one or more of 40 standard architectural style classifications that appear in the National Register Information System (NRIS) database. Other properties are given a custom architectural description with "vernacular" or other qualifiers, and others have no style classification. Many National Register-listed properties do not fit into the several categories listed here, or they fit into more specialized subcategories.