The art of coin collecting is quite complicated and requires a great deal of knowledge. If you aren't familiar with coins, here is a quick overview in simple terms:
Circulated – A coin that has been used as legal tender and shows signs of wear. Most older keepsake family coins are circulated. Even though the money value may not amount to much from a collector standpoint, the sentimental value is priceless. With its unique patina and wear, a circulated coin often causes us to pause and wonder “where has this coin been?”
Almost Uncirculated (AU) – Almost Uncirculated coins refer to coins that have a small amount of wear on its highest points that is usually seen on coins that have had minimal circulation.
Brilliant Uncirculated (BU) – A coin that has never circulated in the regular money supply in the economy. The coin shows no signs of wear on any of its surfaces. It retains all of its original mint luster and the coin’s design remains in sharp relief.
Gem Proof – A coin that was produced by the U.S. Mint to a much higher standard of finish. Originally, proofs were intended as pre-production samples. With the popularity of collecting about two centuries ago, a large number of proofs were sometimes made for sale to collectors. Proof coins are struck on specially adapted coining presses more than once to bring forth the most minute detail with remarkable clarity. Proof coins are “prettier” in that they have a mirror-like shine and very detailed design. Proof coins may or may not be created with 90% Silver.
Cameo Proof – Coins are distinguished from ordinary proof coins in one significant way: the raised parts of a cameo proof coin appear frosted. The plain, flat areas have a mirror-like appearance while the design and lettering actually appear creamy or white. Most proof coins struck since the 1970s are cameo proofs.
Deep Cameo Proof – Cameo coins with devices (design and lettering) that are deep white. The usual deep cameo proof coin may even look black and white. The flat part will look black (due to being deeply polished and highly reflective) and the devices will look white.
Silver Deep Cameo Proof - One of the most valuable of the proof coins, these beautiful coins are made of 90% silver. They typically include the Washington Quarter, Roosevelt Dime, and Kennedy Half Dollar.
Reverse Proof – New to coins is the "reverse proof". They’re manufactured exactly like other proofs with two exceptions. The finish techniques of the background and foreground are swapped. The portrait foreground isn’t frosted but instead mirror-like and the background surface isn’t shiny and mirror-like but instead frosted.