Encyclopedia Of US Coins
A type set is generally defined as a collection that contains one, and only one, of each design for a series or complete coinage series. For example, a complete type set of 3 cent silver will be only 3 pieces while a complete type set of U.S. circulating coins would contain one of each design type from half cents through bullion platinum and from 1792 to the present.
Major design types are usually supplemented with variations such as coins with and without arrows, rays, drapery or mottoes. A complete collection is impossible for all but the most wealthy so compromises and hard choices must be made. Some think that type collecting is the most enjoyable specialty in U.S. coin collecting.
United States Type Coins