Teletext is a medium where encoded pages of information are broadcast alongside a television programme, and can be decoded on-screen by the viewer at the touch of a button. Developed in the UK in the early 1970s, the last British teletext service was discontinued in the mid-2010s but teletext is still used in many countries around the world.
Once broadcast, teletext was generally overwritten on the server and the archive status of teletext pages is patchy at best, with (at least in the UK) only a few examples of pages saved by the broadcasters and some pages saved by the public using PC decoder cards.
This website covers efforts to recover teletext pages from television programmes recorded on regular domestic videotape and other methods.