This is what we found on Wikipedia regarding the Riverdance:

Dance is an art form, consisting of sequences of body movements with aesthetic and often symbolic value, either improvised or purposefully selected. Dance can be categorized and described by its choreography, by its repertoire of movements or by its historical period or place of origin. Dance is typically performed with musical accompaniment, and sometimes with the dancer simultaneously using a musical instrument themselves.

Two common types of group dance are theatrical and participatory dance. Both types of dance may have special functions, whether social, ceremonial, competitive, erotic, martial, sacred or liturgical. Dance is not solely restricted to performance, as dance is used as a form of exercise and occasionally training for other sports and activities. Dance performances and dancing competitions are found across the world exhibiting various different styles and standards.

Dance may also be participated in alone as a form of exercise or self expression. Dancing is common human behaviour, and does not necessarily require specific choreography.