From USDF’s Glossary of judging terms:
RHYTHM The recurring characteristic sequence and timing of footfalls and phases of a gait. For purposes of dressage, the only correct rhythms are those of the pure walk, trot, canter, rein back and piaffe. See also the definition in the Freestyle section.
Note 1: “Rhythm” is sometimes used mistakenly to mean “tempo” (rate of repetition of the rhythm). This usage is not consistent with the correct English definition of “rhythm” (per Webster), nor with its normal usage in music.
Note 2: In English, there is no one term that covers both the rhythm (as defined above) and the tempo, as does the term “Takt” in German. This has caused confusion because “Takt” has commonly been translated as Rhythm. For purposes of the Pyramid of Training, the German term “Takt” is translated as “Rhythm” and is used as shorthand for both the rhythm itself (as defined above) and the suitable rate of repetition of the rhythm (tempo). "
So a 4 beat canter does not have correct rhythm, nor does a lateral walk. And a trot with NO moment of suspension is not correct either.