A comples topic and the practical meaning has changed greatly over time.
Officially they are stamps on a cover that was posted on the first day of issue of that stamp. Many years ago the only to get them was to do it yourself. ie buy the stamps and post then to someone probably yourself and the stamps had the normal post make as used at that time. Of course some were just normal usage that happened to be on the first day. These covers all went through the postal system
Then companies got into the act and started to produce illustrated covers for the stamps and at the same time they would apply the stamps and post them to you. At a cost of course !
Later the post offices started to use special cancellations on the first day of issue.
All this progressed and the post offices saw it was a source of revenue and got more organised. They produced lost of covers with the new issues on the, cancelled them with a postmark dated the day of issue and then sent them to the customer. Almost always in another envelope so the FDC did not get damaged. These covers did / do not go through the post as you might expect as they were sent inside another envelope. With high demand these could not be prepared ont eh day of actual issue of the stamps and so were / are made up before the actual day of issue or even after the day.
First day covers of older issues can be valuable the earlier the better they start to become more expensive if they date before WW2 or so and it probably depends on the country. Modern covers have a lot less resale value than the cost original cost. In the UK modern FDCs are typically sold at stamp fairs almost by the box load. As the stamps tend to have specuial distinctive cancellations this can also reduce their value compared to genuinly used stamps which actually fulfilled there postal.purpose
In short, a cover (envelope) with stamps stuck on and posted on the day the stamps were issued - which will be then get a postmark/cancel bearing that date.
As said above, this has moved on to become a whole industry of specially manufactured covers, special postmarks, all sorts of clever things.
Disclaimer: While a tremendous amount of effort goes into ensuring the accuracy of the information contained in this site, Stamp Community assumes no liability for errors. Copyright 2005 - 2026 Stamp Community Family - All rights reserved worldwide. Use of any images or content on this website without prior written permission of Stamp Community or the original lender is strictly prohibited. Privacy Policy / Terms of UseAdvertise Here