A Multiple Anime TCG is an old term used to categorize TCGs that featured more than one anime, manga or video game series.
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Both of these terms are now outdated since the TCG community has expanded outside of the anime and manga categories.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 Multiple 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.