Se-tenant : An attached pair, strip or block of stamps that differ in design, value or surcharge.

Secret Marks : Many stamps have included tiny reference points in their designs to foil attempts at counterfeiting and to differentiate issues.

Self-adhesive Stamp : A stamp which is peeled from a sheet and is ready with a pressure-sensitive adhesive.

Selvage : The unprinted paper around panes of stamps, sometimes called the margin.

Semi postal Stamp : A First-Class Mail stamp priced to include an additional charge earmarked for a specific purpose, e.g., breast cancer research.

Series : A number of individual stamps or sets of stamps having a common purpose or theme, issued over an extended periods of time (generally a year or more), including all variations of design and/or denomination.

Set : A group of stamps with a common design or theme issued at one time for a common purpose or over a limited period of time (generally less than a year).

Shade : A stamp that has a slight difference in color.

Souvenir Sheet : A small sheet of stamps with a commemorative inscription.

Space filler : A stamp which is not of high quality used to fill a space in an album where one of high quality is difficult to obtain.

Special Issues : Stamps with a commemorative appearance that supplement definitive and meet specific needs. These include Christmas, Love, Holiday Celebrations, Airmail, Express Mail, and Priority Mail stamps.

Specimen : A stamp used as an 'example' and overprinted as such.

Stamped Envelope : A mailable envelope with postage embossed or imprinted on it.

S.T.C : Stated to Catalogue. The term used by auctioneers for lots where the vendor has calculated the Catalogue value. The auctioneer does not bear any responsibility for this statement.

Strip : Three or more unseparated stamps in a row.

Surcharge : An overprint that alters the denomination of a stamp from its original face value.