The Internet has got everything, including a website dedicated to television test cards. Wait, what are test cards?
In the early days of television, there was a need to test the response of cameras then in operation. This was done by use of a special pattern, drawn on to a large piece of card, which the camera then pointed at. Hence the name "Test Card". In the UK, this name has stuck despite most of the patterns now being produced by other means, either transparencies, monoscope or electronically generated. North America has tended to use the term "Test Pattern". Very early, simple patterns used in Britain were sometimes known as "Test Graphs". Test Cards were often 3ft wide, to enable lots of detail to be drawn in. Later versions used clever photographic techniques to produce the final result.