You can find most popular coin collecting phrases in this coin glossary.
tail - the reverse or back side of a coin
third party grading - third party grading services will grade and/or certify coins as genuine. Often the coin will be encapsulated in a plastic holder (or slab) by the grading service to protect it. Called "third party" grading when the service is independent of any dealer or collector's influence. They provide a grading opinion based on established criteria. Examples may include PCGS, NGC, and ANACS.
three cent piece - common term used for the US coin with the value of three cents. Two different metals were used for these coins back in the 1800's. Prior to 1865 the US made three cent pieces out of an alloy of mostly silver. Hence the name "three cent silver". The public complained because the 3 cent silvers were small and thin. By 1865 the US government changed the composition and design of the three cent coins. Three cent nickels were made of 75% copper and 25% nickel from 1865 to 1889. From the looks of the coin you would think it was made out of pure nickel. They were larger and thicker than the three cent silvers. Hence the name "three cent nickel".
token - Something that looks like a coin, but is not legal tender issued by an official government. For example, parking tokens, video game machine tokens, and casino tokens. Some coin collectors shy away from collecting tokens. However, there are a few small groups of serious token collectors.
toning - Shading of color on coins. Toning can be in many forms from dark or brown to various shade of other colors. It can cover the whole coin or more often part of the coin. Toning results when the surface of the coin comes in contact with the air and environment it is exposed to. Traces of material in the metals will also play a roll in toning. Some think toning makes a "protective" coating over the surface of a coin that helps the coin resist corrosion. Toning can be even be artifically done by exposing the coin to certain reactive substances. Some "naturally" occurring toned coins bring a premium in the collector market due to their unique beauty. Others may bring less than an un-toned coin when the toning is unattractive. Also see "corrosion".
troy ounce - a weigh to measure weight. Differs from a regular "grocery store" ounce.
two bits - see "bits"
two by two - nickname for a typical holder for one coin. Measures 2 inches by 2 inches. Often made of cardboard with a clear mylar material in the center. Cardboard 2x2s are not the best way to store coins for the long term.
two cent piece - a US coin with the value of two cents. Common term used for the copper Shield design two-cent coin made from 1864 to 1873.
type - coins containing the same or a similar characteristic. Often in a type collection or set the dates do not matter. Rather the collector is interested in obtaining one of each representative design. For example a collector may want one of each "type" of coin in US circulation today. Such a type set would consist of a cent, nickel, dime, quarter, half, and dollar. A collector may decide to collect one representative of each type of coin by size. For example, a cent type set may include a Lincoln Memorial cent, wheat back cent, indian cent, etc.
type set - collection of coins of one denomination. For example, a Quarter type set would consist of one of each design of quarter that the mint has made. (Dates and mint marks usually are not of concern.)