What term refers to the arrangement of beats into groups of equal size?

The term that refers to the arrangement of beats into groups of equal size is meter. Meter is a fundamental aspect of music that provides a structured way to organize the beat, typically categorized into measures or bars. Each measure contains a specific number of beats, and these beats are grouped in a consistent pattern, which can be seen in various time signatures such as 4/4, 3/4, or 6/8.

Understanding meter is essential for performers and composers, as it influences the flow and overall feel of the music. This underlying structure helps musicians know when to place emphasis on certain beats, enabling them to convey different emotional qualities or styles.

Rhythm, while closely related to meter, refers more broadly to the timing of notes and how they are arranged in relation to the beat but does not specifically pertain to the grouping of beats themselves. Tempo is concerned with the speed of the music, indicating how fast or slow a piece should be played, while tempo marking is a specific indication of tempo that informs the performer of the desired speed but doesn't address beat arrangement. Thus, the defined structure of meter allows for a cohesive musical experience through its grouping of beats.