Toning shoes are shoes that are unstable and are designed to give the body an additional tone up when using them. The unstable design features include concepts like rocker soles. These designs alter the biomechanics of the limb so that muscles are used in different ways and the gait or walking technique is different. It is this alteration in the bioemchanics that make the toning shoes useful to to users.
There plenty of debate if toning shoes actually give you a tone up or not. Some studies show that the toning shoes do not alter muscle function and other studies show that they do. It does appear that the individual response to these type of shoes is very individual, so they will help some people and not help others.