the basic rhythmic unit in a piece of music
"the piece has a fast rhythm"
"the conductor set the beat"
recurring at regular intervals
"The traffic lights operate on a strict rhythm, changing color every thirty seconds without fail."
the arrangement of spoken words alternating stressed and unstressed elements
"the rhythm of Frost's poetry"
natural family planning in which ovulation is assumed to occur 14 days before the onset of a period (the fertile period would be assumed to extend from day 10 through day 18 of her cycle)
"She relied on rhythm methods by abstaining from intercourse between the tenth and eighteenth days of her menstrual cycle."
The variation of strong and weak elements (such as duration, accent) of sounds, notably in speech or music, over time; a beat or meter.
"The drummer adjusted the tempo to match the rhythmic pulse of the song's melody."
In plain English: Rhythm is the steady pattern of beats that makes music feel moving and organized.
"The drummer tapped his foot to keep up with the rhythm of the song."
Usage: Rhythm refers to the patterned flow of stressed and unstressed beats that creates structure in both speech and music. Unlike a steady tempo, rhythm involves the specific variation in timing between these elements to produce a sense of movement.
The word "rhythm" was first coined in English in 1557 via the Latin rhythmus. It ultimately traces back to an Ancient Greek root meaning "to flow," reflecting its original sense of any measured movement or symmetry.