Altered Surfaces is sometimes used as a catch all term by grading companies when choosing not to grade a coin. This can be due to the coin being cleaned/dipped, artificially toned, PVC or foreign material on the coin.
There are “Coin Doctors” out there who use auto body putty to fill in bag marks, cracks, and other unwanted damage. Then a layer of paint is applied to give the coin that frosty look we all love. This is done to try to trick the grading companies (and those who will buy the coin) to give the coin a higher grade than the coin would normally receive.
Some vamworld.com users have been successful at resubmitting a coin that came back as an Altered Surface coin and getting it successfully graded after a second, third, and sometimes even a fourth or fifth attempt at sending it in. So do not necessarily give up on a coin which comes back as Altered Surfaces. Persistence is the key if you truly believe your coin is "original". Below are some visual examples of real Altered Surface coins.
Please click this link for the full VAMworld.com definitions page.