What does CC mean on a Morgan silver dollar?

It is the mintmark and signifies that the coin was minted in Carson City, Nevada. On a Morgan dollar, the mintmark would be located on the reverse (back) of the coin, below the eagle's tail feathers. Other potential mintmarks on a Morgan dollar would be "S" (for San Franscisco), "O" (for New Orleans) and, in 1921 only, "D" (for Denver). A lack of mintmark signifies that the coin was minted in Philadelphia. Note that the Carson City and New Orleans mints are no longer operational. The mints still producing coins in the United States are Philadelphia ("P", except on pennies, in which case there is no mintmark), Denver ("D"), San Francisco ("S") and West Point. New York ("W"). San Francisco only produces proof coins at this point (very highly polished and well struck versions of coins for collectors), and possibly bullion and commemoratives, and West Point only has every produced bullion and commemorative coins (except for a Roosevelt dime in 1996).