MNH means Mint - Never Hinged. That means the original gum is intact and has not been damaged by the use of a hinge, a mounting method that can leave residue and remove some of the original gum.
Imperf is the abbreviations for Imperforate. Perforations are the holes or cuts made to allow you to separate stamps in a sheet or roll. Imperforate means that the stamp is either intentionally made...
CTO stands for Canceled To Order. Countries that produced large quantities of stamps for the collector market, not intending them to be used for real postage, canceled the stamps during the printing...
OG means Original Gum. This indicates the stamp has never been used and has been kept away from moisture so that the gum applied when the stamp was made is still intact.
Tagged refers to a method of marking a stamp so that automatic mail machines can work with a letter. Early trials included graphite lines on the back of stamps. Today, most stamps are tagged with a...
Tagging is a phosphorus ink often applied to the stamps to allow automated machines to handle the mail. Mottled means that it is not an entire covering, but that the ink has blotched.