What is the definition of proof coins?

Proof coins are initial samples of production runs of coins. They have traditionally been made to test the cutting and shaping tools used in the coin's manufacture, but as coin collecting has risen in popularity, greater numbers have been created simply to satisfy collector demand.

Proof coins often have special qualities that differentiate them from the regular production runs of that coin type. They frequently have more of a noticeable contrast between the raised areas where the designs are printed and the flat, blank areas. They are also sometimes treated to have a frosted or mirrored appearance. Proof coins also have variations in their appearance and quality and are assigned different grades in the same manner as other types of coins.