1. Movement or variation characterized by the regular recurrence or alternation of different quantities or conditions: the rhythm of the tides.
2. The patterned, recurring alternations of contrasting elements of sound or speech.
3. Music.
   1. The pattern of musical movement through time.
   2. A specific kind of such a pattern, formed by a series of notes differing in duration and stress: a waltz rhythm.
   3. A group of instruments supplying the rhythm in a band.
4. 1. The pattern or flow of sound created by the arrangement of stressed and unstressed syllables in accentual verse or of long and short syllables in quantitative verse.
   2. The similar but less formal sequence of sounds in prose.
   3. A specific kind of metrical pattern or flow: iambic rhythm.
5. 1. The sense of temporal development created in a work of literature or a film by the arrangement of formal elements such as the length of scenes, the nature and amount of dialogue, or the repetition of motifs.
   2. A regular or harmonious pattern created by lines, forms, and colors in painting, sculpture, and other visual arts.
6. The pattern of development produced in a literary or dramatic work by repetition of elements such as words, phrases, incidents, themes, images, and symbols.
7. Procedure or routine characterized by regularly recurring elements, activities, or factors: the rhythm of civilization; the rhythm of the lengthy negotiations.

In simple terms, rhythm is a word that refers to the length of each note in a piece of music. This means that if you take a song that you know and say the words in time with clapping, you will be clapping the rhythm.

“Rhythm” must not be confused with “beat” or “pulse”. The beat of the music is a regular pulse (like the regular pulse of someone’s heartbeat). Music may feel as if it is going 1-2-1-2 or 1-2-3-1-2-3 or 1-2-3-4-1-2-3-4. When we write the music down we put each group in bars (or “measures”). The first beat of the bar feels stronger than the others.

All musicians have to have a good sense of rhythm. To play or sing rhythmically they must keep a steady beat in their head (if playing alone), listen to the others players (if playing in groups) or watch the conductor (if there is one).

People who are playing on their own can practise with a metronome to help them to play to a steady beat. However, musicians also use rubato (rhythmic freedom), especially when playing music of a romantic nature. One has to learn to let the music “breathe” in the right way. This is not the same as playing unrhythmically (badly). It is something one learns with experience.

Sometimes the word rhythm is used in a more general sense to mean the general flow of the music, or of life in general ("the rhythm of life").