If you are thinking about starting a hobby of coin collecting, you need to have a few definitions of key terms. Some of these terms are relative, while others are comparative. The most basic one is rarity, which can be further modified by numbers and adjectives. However, it is important to keep in mind that there is no universal scale for coin rarity. In order to get a better idea, you can look up a price guide, such as A Guide Book of United States Coins, which has a red cover and lists retail prices for different coins.
Another term used for coins is counterfeit, which is a piece of coin that was forged to mimic a genuine numismatic piece. These coins are not only illegal, but are often used for monetary or numismatic fraud. They include most silver and nickel alloy coins. Another term used to describe counterfeit coins is multiple crowns, which are coins whose diameters are greater than 43 millimeters. The word multiple crowns is usually used by government, but it is not exclusive to it.
Another coin collecting definition is assemblage, which refers to a collection of coins. An accumulation may be random, as in a monetary hoard, or it may refer to a specific type or series. For example, an assemblage may consist of an entire set of $1 bills. This is particularly true of the Original Series and the 1875 series of the $1 National Bank Note.