Ron Guth: From time to time, the United States Mint considers implementing new designs on the coins in circulation. Historically, the Mint developed new designs either internally or through outside competitions. As the selection process narrowed, actual sample coins were made of the various designs. These "Pattern" coins allowed Mint officials to see how the proposed designs would look in three-dimensional relief, to test for any problems in producing the coins, and to try out new metal alloys.
Pattern coins fall into a number of different categories: 1. Both sides were rejected for use on circulating coins. 2. One or both sides were modified slightly before they were used on circulating coins. 3. Either the obverse or the reverse was accepted for use on circulating coins. 4. Both sides were accepted for use on circulating coins, but the metal composition may be different from the one eventually used.
Die Trials were tests of dies in various stages of production. Back when dies were "cut" by hand, the engraver would periodically stamp the die into a piece of soft metal to see how the work was progressing (these are generally uniface stampings on oversized or irregularly shaped blanks). Die Trials may include "setup" pieces which were used to determine proper die alignments and striking pressures before regular production began.
Fantasy Coins include unexpected pairings of mis-matched dies made by Mint officials to create artificial rarities for personal gain or at the request of collectors. Fantasy Coins include the so-called "Restrikes" that were made outside the Mint from discarded dies, often combining dies of different types and vastly different dates.
Sometimes, the line between Patterns, Die Trials, and Fantasy Coins becomes blurred. In many cases, we simply lack the information as to when a coin was struck, why, and by whom. Often, we must turn to the coins themselves to look for such clues and, thankfully, the coins are willing to help.
Is it important that we classify these coins properly? Yes, because apart from our natural human tendency to categorize, pigeon-hole, and classify just about everything around us, most collectors are concerned about a thing called "intent". Rarities that were "made-to-order" or that were created deliberately hold less of an attraction than legitimate rarities, and justly so.