Part of starting a coin collection is to learn about the terms it uses. It’s important to learn this because you’ll eventually be going to coin shows and deal with coin dealers, so you want to know your stuff.

Coin Terms is a language understood by true numismatists; and you can’t call yourself one if you don’t know these definitions by heart.

So here are a few, easy to remember definitions that are commonly used in the coin industry:

ASSAY
This is a process to test the weight and purity of a coin by using scientific means. This is usually done to determine if the coin contains the proper purity and amounts of precious metal it should have.

BULLION
This refers to items made of precious metal (silver, gold, and platinum). Bullion are usually in the form of ingots, bars, rounds, and coins. The bullion value of a coin will depend on the “value of the metal” a coin contains.

CERTIFIED COIN
These are coins that have been certified by one of the third party grading services – PCGS, NGC, ANACS/ICG. Having been certified licenses the coins as genuine. A certified coin should be accompanied by a photograph certificate or sealed in a special plastic slab. Often a certified coin is accompanied by a photograph certificate or is sealed in a special plastic slab.

DOUBLE EAGLE (U.S.A)
This term is used to describe a $20 gold pieces widely made from 1849 to 1933. It’s called a double eagle because the coin’s gold content back in the day was twice that of an “eagle” or $10 gold piece. Each double eagle gold coin would “almost” contain a full ounce of pure gold.

ERROR COIN
These are coins with defects that escaped the careful eyes of the quality control of the US mint inspectors during production. Nowadays, error coins are kept from being released as part of the modern production procedure.

FILLER
These are coins that are in poor or average quality, in which the collector decided to keep for its rarity; but only until they find a similar coin with better quality.

GEM
This is used to describe a coin with exceptionally high quality.

HAIRLINES
Not the same hair lines as you’re thinking – these lines are very light scratches on the surface of a coin. Typical on proof coins, hairlines are usually caused by light cleaning, polishing or light contact with plastic flips or plastic slides.

INSCRIPTION
These are lettering or wordings stamped on a coin.

JUNK SILVER
This is an informal term to describe silver coins (in fair condition) that has “no numismatic or collectible value above the bullion value of the silver it contains“. This term is usually used in USA, UK, Canada, and Australia.

KEY DATE
A slang term in coin collecting which means indicates a rarest date and mint mark of a particular coin series. These coins are usually more difficult to find, of lower mintage, or more expensive.

LETTERED EDGE
It is the outside edge of a coin with inscription. The lettering is usually embossed, but sometimes “incused”.

MINT
This is a place or facility where coins are manufactured. Mint facilities would produce coins under the authority of a government; however, there are private mints that can also produce medals and coins for other countries that cannot afford their own minting facilities.

NUMISMATICS
A scientific study of all the aspects of currency, the person who specializes in this study is called a numismatist. In coin collecting terms, a Numismatic is a study of coin collecting and a numismatist is a coin collector.

OBSOLETE
A term used to describe coin design or series that  is no longer being produced by mints.

PR(quality of coin in number)
PR stands as an abbreviation for “proof”. The number that follow should indicate the quality of a coin. For example: PR60. The quality number runs from 1-70, with 70 being the highest or absolute perfection.

QUARTER EAGLE
If a “Double Eagle” equals a $20 gold coin; an “Eagle” equals a $10 gold coin; a “Half Eagle” equals a $5 gold coin, then a “Quarter Eagle” would equal a $2.50 US gold coin.

REVERSE
Sometimes called “tails”, it is the backs side of a coin.

SPLIT GRADE
Split grade is where you place a different amount for the front and back of a coin. This occurs when a coin has a different condition for its obverse (front of the coin) and reverse (back of the coin). For example the obverse would have no scratches, while the obverse have a few ones or is in bad quality.

TYPE
These are coins collected that contain the same or similar characteristics; where dates would often be irrelevant.

unc, unk or UN
These are abbreviation for uncirculated coin or Mint State coin. Uncirculated coins are those that has never been circulated and retained its original luster.

VEST POCKET DEALER

A coin dealer who does not own a shop or a store, and does not set up at coin shows. Many coin dealers started out as a vest pocket dealer.

WHITMAN
Whitman produces many coin collector’s books, albums, and collecting supplies. They are also know as Whitman Publishing company.

YEAR SET
Coins that are collected because of its year (date of manufacture), rather than its mint mark. A coin collector can collect as many year set as he want, or only collect coins from a specific year.

Sources:

http://cointerms.com/glossary/1stpage-of-definitions.htm
http://www.coin-collecting-guide-for-beginners.com/coin-collecting-terms.html#C