AE – Short for Aeratus, Latin for copper.
 
AR – Short for Argentum, Latin for silver.
 
AU or AV – Short for Aurum, Latin for gold.
 
Billon – Any alloy made up chiefly of base metals which contains a negligible amount of silver.
 
Celator – The craftsman in charge of creating the dies.
 
Die – The metal stamp used to impress a design onto a metal blank. Each coin is made using two dies for obverse and reverse. Die axis refers to the position of each die relative to each other when the coin was struck.
 
Exergue – Generally taken to mean the bottom part of the coin. This area is usually delineated and reserved for codes unrelated to the rest of the coin 's design or message.  The exception are the Denarii and Aurei which sometimes use the exergue as extra spacing to accommodate large reverse legends. In most other cases the exergue is used for mint marks. These mintmarks often spill into the reverse fields as well. While not frequently used, the obverse sometimes will have some exergue writing.
 
Fabric – Refers to the texture of a coin. Two coins with identical designs can still have a very different "look and feel" about them. Factors like thickness, metal type, porosity, waviness and so on make up a unique signature for each coin that becomes associated with a particular culture and era. The study of a coin 's fabric is vitally important in determining a coin‟s authenticity.
 
Flan – The metal blank used to make the coin. The term‟s use is synonymous with "coin" except that the former concerns itself only with the structural integrity, shape and makeup of the metal.
 
Fourree – A French word meaning „stuffed‟. In numismatics it refers to an ancient counterfeit meant to deceive the recipient of the coin, not a modern collector. The counterfeiter would use a copper core and coat it in silver before striking it and attempting to pass it off as a good coin. The artistic merit of Roman fourrees is usually so good that they can only be identified when the silver coating has worn through enough to reveal its interior. Given this fact it is suspected that the counterfeiters could only have been mint officials with access to official dies and/or under covert approval of their superiors. Gold fourrees exist as well.
 
 
Mule – (or hybrid) A term used to describe a coin whose obverse is mismatched with the reverse. For example, the Julia Domna Denarius pictured below is of a military type belonging to her husband Septimius Severus and which would never ordinarily be featured on a coin of an empress.
 
 
Mules are particularly abundant during transitional periods as one emperor is replaced with another and dies used for the former become mixed with the latter out of carelessness, haste or both. 
 
Obverse – The front or "heads" of a coin.
 
Orichalcum – A naturally occurring brassy alloy mined on the Italian peninsula. It was used irregularly in the minting of Sestertii and Dupondii during the first and second centuries. Being of a naturally golden color, coins made of this alloy are often mistaken for gold by inexperienced collectors.
 
Patina – Copper-based alloys and to a lesser extent silver ones exposed to the environment become corroded over time. If this environment is not too severe only the coin 's surface becomes affected. This superficial layer is called a patina and novice collectors may often attempt to remove it in the failed hopes of restoring the coin to an as-new condition. A patina is usually desirable to maintain as it forms an effective barrier against further corrosion and is often considered quite attractive.
 
 
 
Reverse – The "tails" side of the coin.
 
Style – The unique artistic attributes of a coin‟s design. The art of engraving is remarkably consistent for a particular age and becomes a mint 's signature as its various students learn to mimic one another‟s renderings. While each mint 's output becomes consistent with itself it is often dissimilar to other mints‟ coins. The farther apart any two mints are the more likely that the artistic style will be different even when the overall design of the artwork and epigraphy is the same.
 

Style also evolves over time within a mint and this, too, becomes a familiar signature. In conjunction with the study of fabric as mentioned above an understanding of style is essential in distinguishing authentic from fake.