Definition: An SMS coin is a coin that was in a U.S. Mint Set issued during the years 1965, 1966, and 1967. The U.S. Mint didn't strike Proof coins during these three years, so they issued Special Mint Sets (SMS sets) instead. SMS sets contain higher than normal quality coins which can be told apart from regular Uncirculated coins of the same year. SMS set coins are often sold individually, but they are not particularly rare, despite the fancy name. Mintages of the SMS coins are as follows:
1965 SMS coins - 2,360,000
1966 SMS coins - 2,261,583
1967 SMS coins - 1,863,344
Sellers on eBay are always trying to get more money for SMS coins
than they're really worth, just because the name "Special Mint Set" sounds valuable.