Postage Stamps available are not necessarily always rectangular in shape. There's triangular in addition to circular types on the market as well as pentagonal.
You can find different kinds of postage stamps which are used to signify that postage s paid for. Here ther are below:
Airmail Postage: The word airmail appears on the stamp plus they are often larger than the regular postage stamps used for the envelopes. Just like the daily stamps each one does provide a name of the place along with the price paid.
Coil postage stamps: These include postage stamps which you can shop for via a vending machines. You rip off a postage stamp on the coil when you want to use one.
Commemorative Postage Stamps: they are postage stamps issued by nations around the world to remember a unique event which happens in the country. There could be lots of these within one year, but they are just for sale in small quantities.
Definitive Stamps: Examples of these are your key postage stamps which are used by the same state so are produced and then reprinted in bulk. They come in several different denominations that would be needed to make-up the postage needed to post mail.
Express Mail Stamps: These include Postage Stamps used for mail that needs to turn up in an exceedingly short period of time. Presently there are envelopes for this reason that contains the postage necessary.
Army Postage Stamps; The Military of nations around the world have got its personal official stamp to use on the mail that they send.
Official Stamps: Mainly government departments and also bureaus can use these postage stamps which can be issued by the government authorities of their nations.