What is the name of the 20th-century social dance that has no fixed step pattern?

The 20th-century social dance that has no fixed step pattern is known for its improvisational quality, allowing dancers to express themselves freely rather than adhering to a strict set of steps. This characteristic is particularly prominent in certain social dances that emerged during the 20th century, which were heavily influenced by various cultural movements and societal changes.

The other dances listed, such as the tango, cha-cha, and rumba, are characterized by their specific step patterns and sequences, which are essential to their traditional forms. While these dances may allow for some degree of personal interpretation and style, they fundamentally rely on established steps and rhythms that define their execution. In contrast, the dance in question encourages spontaneity and creativity, reflecting the social dynamics and cultural influences of its time.