Real Dictionary

rhythm
countable noun: A rhythm is a regular pattern of changes, for example changes in your body, in the seasons, or in the tides.
variable noun: A rhythm is a regular series of sounds or movements.

rhythm in American English
flow, movement, procedure, etc. characterized by basically regular recurrence of elements or features, as beat, or accent, in alternation with opposite or different elements or features
noun: movement or procedure with uniform or patterned recurrence of a beat, accent, or the like

rhythm in British English
noun: the arrangement of the relative durations of and accents on the notes of a melody, usually laid out into regular groups (bars) of beats, the first beat of each bar carrying the stress