A collector coin is a type of coin that is sought after by collectors due to its rarity or historical significance. The term 'collector coin' can be broken down into three parts: METER (5 letters), SOFA (4 letters), and SLOT (4 letters). METER refers to the measurement of a coin's diameter, SOFA is an acronym for the Society of Numismatic and Financial Analysts, and SLOT is a reference to the groove in which a coin is placed when it is stored.