A Single Anime TCG is an old term used to categorize TCGs that featured only one series that falls under the Anime, Manga or Video Game categories.
This differentiation was used primarily because many early TCGs were almost entirely centered around Anime and Manga. Because of this most TCGs were classified as either a Single Anime TCG or Multiple Anime TCG.
Both of these terms are now outdated since the TCG community has expanded outside of the anime and manga categories.
Modern Day Single Anime TCGs are simply referred to as Anime TCGs. A TCG that includes Anime and Manga are sometimes referred to as Animanga TCGs. A TCG that includes Anime, Manga and Video games are referred to as Animangame TCGs.
Single Anime TCGs have been dying out in recent years, as many TCGs owners prefer to offer a wider variety of series in order to attract more members. There is still the occasional TCG dedicated to a single anime or game series that pops up but it is very rare.
The first official Single Anime TCG was Senshi Card-Mania!, a Sailor Moon TCG.