Postal cards:Postal cards are postal stationery and have a printed or embossed indicium and are sold by governmental postal authorities. In the United States, they were first produced in 1873. Some of the forms taken by postal cards include the regular single card, the attached message-reply cards, airmail postal cards, and official postal cards used for official government business with a “penalty for private use”. Pstcards,on the other hand, are cards prepared by private companies that do not have prepaid franking and readily available at commercial outlets. They are frequently illustrated with pictures or printed advertisements. They are generally not considered postal stationery.
Registered envelopes:A strong envelope with an imprinted stamp sold only for use with the registered mail service. Confusingly, these are usually marked Registered Letter but that term strictly only relates to a normal letter or packet that has extra postage and markings applied so that it may travel under the registered mail service.
Stamped Envelopes: The envelope form may be called a stamped envelope or, alternatively, a postal stationery envelope (PSE for short). In August 1852 an act of the U.S. Congress authorized the Postmaster General to provide “suitable letter envelopes with such watermarks or other guards against counterfeits with the addition of the value or denomination of the postage stamps so printed or impressed thereon…”. The first result was the 1853 Nesbitt issues of stamped envelopes, named after the contractor who produced them for the government. Considering the different envelope sizes, knives , colors, dies to print the indicia, and denominations there are literally thousands of different stamped envelopes produced for the US.