In the simplest case, you have a dual tuner. This is able to convert signals from two different sources (usually aerial and cable) into images!
Twin tuner.
With a twin tuner, it's not so much about the sources, but more about the possibilities: It can receive two channels simultaneously and thus, for example, show a film while another one is being recorded in the background!
Hello gheini Have a look at "https://www.giga.de" where the difference is explained. It is not the same on this page! It serves different purposes. Greetings Wolfgang