An Uncirculated coin usually means a coin that has never been circulated, a coin that is in "Mint State." This means the coin is just as minted, with absolutely no wear on it at all (although bag marks are okay.)
Throughout most of the history of coin collecting, the term Uncirculated has always been clear; it meant a coin that had never been circulated. However, in 2005 the U.S. Mint made a change to the finish on the coins in its annual "Uncirculated Mint Sets" to give the coins a distinctive burnished, or so-called "Satin Finish" appearance. Because the Mint continues to use the term "Uncirculated" to describe Satin Finish coins, despite objections from the hobby, there is much confusion in the current coin collecting marketplace among new collectors regarding this term.
The easiest way to solve the confusion is to avoid using the term "Uncirculated" altogether. Current coin grading standards call a coin that has never been circulated "Mint State," so "Mint State" is the term that should be used to describe such coins. If you are describing a coin that has the burnished appearance, refer to it as "burnished" or "Satin Finish." This way, you are clearly describing the coin in a non-confusing manner.
If I say I have an Uncirculated coin dated 2008, I might be describing either a coin that is in Mint State, or a coin that has a burnished appearance, so it is best to avoid using the term Uncirculated at all.