The term "slotta" refers to the basing of a miniature in the tabletop community. More specifically, a slotta model is a model which has a strip of metal at the bottom, usually with information such as copyright, manufacturer, date, and sometimes the sculptor on it. This metal or plastic tab slips into a slot on the intended base.
Originally, all models were either meant to stand up kn their own or came attached to their own base, as part of the model. These had issues such as increasing expenses (as most models were metal in those days, effectively doubling the amount of metal needed for some minis) and taking effort to remove for dioramas. An unpopular later innovation was pegs on the feet of models that fit info a separate base, usually plastic. However these pegs were hard to fit into some bases, and had to be sculpted for each miniature in some cases.
Both incorporated and peg bases are now called "Pre-slotta" by the gaming community.
In 1985, Games Workshop released the first slotta bases through Citadel Miniatures. They were advertised as a massive innovation in the tabletop gaming community, and by all rights they really were. Soon many companies switched to slotta bases, although some like Ral Partha continued making incorporated bases.