Polytonality is the use in music of several keys at the same time. Music such as this is called polytonal.
Bitonality is the use in music of two keys at the same time. Music such as this is called bitonal.
Most traditional music is "in a particular key" e.g. in "C major" or in "D major" or in "D minor". Music that is in C major uses the notes of a C major scale.