Use the noun rhythm to refer to the regular pattern of something in a cycle or the beat in a song. In the summer, your life takes on a different rhythm than during the school year.
Rhythm comes from the Greek rhythmos "measured movement, flow." The beat of a song or the meter of a poem is its rhythm. You can also describe the cycle of things that happen in life or nature like the ocean tide or the passing of the seasons as a rhythm. If you have no rhythm, you're not very good at dancing. And once your favorite basketball team has found its rhythm, you know it's going to win.