MNH (mint, never-hinged) >>> Mint stamp with full original gum (or no gum if that was the way it was issued) that has never been hinged and has no other gum disturbances.
MLH (mint, light hinge mark) >>> Mint stamp with full gum that has been hinged but the mark left behind is light or small.
Mint >>> Mint stamp with full gum that has been hinged and the mark left behind is large/prominent or a portion of the hinge remains (hinge remnant). Also includes other gum disturbances as described, for example, fingerprints, paper adherences, gum pulls from being stuck down to page.
MNG (mint, no gum) >>> An uncancelled stamp that has no gum when it was originally issued with gum. It could have been used for postage but escaped cancellation, or the gum could have been washed off due to sticking to pages or toning.
CTO (cancelled to order) >>> A mint stamp with full original gum that has been cancelled by a postal authority. The stamp has not been used as postage. Some used stamps may be CTO, as once the gum is removed it is often difficult to determine the difference.
Used >>> A stamp that has been used as postage and has been cancelled by a postal authority. When one scan is used to represent multiple copies of a used stamp, the least attractive example of the group is used. Thus, the stamp you receive will be of equivalent or better quality.
blk (block) >>> An unsevered, even-numbered group of stamps.
cds (circular date stamp) >>> A type of cancellation that is a circular and has the date within the cancellation. When the term is applied to used stamps, the date is visible on the stamp.
FDI (first day of issue) >>> Used to describe an official, first day of issue postmark.
FDC (first day cover) >>> An envelope bearing a stamp and official, first day of issue postmark (FDI). Usually the envelope is illustrated to reflect the nature of the stamp issue.
MS (miniature sheet) >>> A small sheet of one or several stamps, usually with a decorative margins, issued as a souvenir for collectors.
Opt (overprint) >>> Any printing over the original design of a stamp.
perf (perforation) >>> Holes punched between stamps in sheets to enable easy separation. There are various kinds and sizes or perforations which are measured by a perforation gauge. Often, stamps of the same design have different perforation sizes and variation in stamp value can result.
Pmk (postmark) >>> Any mark cancelling the stamp.
POP (post office pack) >>> A pack (folder or book) prepared by a postal authority that contains stamps and written information about the issue.
SG (Stanley Gibbons) >>> Prefaces a number to indicate Stanley Gibbons catalogue number eg SG 125.
Sc (Scott) >>> Prefaces a number to indicate Scott catalogue number eg Sc 125
Wmk (watermark) >>> When paper is thinned during production to produce a semi-transparent pattern or design of some kind.