Taikenban (体験版 or 体験盤) are demonstration softwares (demos) or trial versions of games. It includes playable and non-playable softwares (movie CDs, as an example). Some are included with retail games as bonus discs, some are demos offered in magazines, some others are single softwares given for free during promotional campaigns to gamers, stores, lottery applicants... Most of the Playstation hibaihin set is composed of them!
I've tried to make a classification as clear and comprehensive as possible, it was a big job...
Please note :
Many taikenban have several variants : they are grouped in family pictures and posted together in the Showcase section.