Polytonality is the musical use of more than one key simultaneously. Bitonality is the use of only two different keys at the same time. Polyvalence is the use of more than one harmonic function, from the same key, at the same time.

What is a bitonal in music?

: using two musical tonalities simultaneously.

What is poly harmony in music?

: a harmonic structure that characteristically introduces two or more simultaneous musical harmonies or strata of harmony.