Rameau can refer to several different things depending on the context.
Jean-Philippe Rameau (1683–1764): A French composer and music theorist of the Baroque music era. He is primarily known for his work in French harpsichord music, operas, and chamber music. His theoretical works also had a significant impact on Western music.
Rameaus theory of harmony: This refers to Rameaus music theory, specifically his idea of the fundamental bass, which was the seventeenth-century precursor to the concept of root position in modern tonal music theory.
Rameau (crater): A small lunar impact crater on the far side of the Moon. It is named after Jean-Philippe Rameau.
Rameau in French could also be translated as branch (from a tree).
So, the term Rameau could represent a person, a theory, a lunar crater, or a branch of a tree, depending on the context.