A scale in which all the steps are whole tones.
A C whole tone scale, for example, would be C, D, E, F#, G#, Bb.

The whole tone scale is a symmetric scale.

Note for improvisors: The first, third and fifth degrees of this scale form an augmented triad, so this is a good scale to play over augmented chords. (The sixth degree is the seventh of the chord, so it should be played over augmented seventh chords.) This scale was used extensively by John Coltrane, especially for ultra-fast licks.