A time signature is a musical notation that indicates how many beats are in each measure and what note value is considered one beat. It is typically written at the beginning of a piece of music and consists of two numbers, one on top of the other. The top number shows the number of beats per measure, while the bottom number indicates the note value that represents one beat, such as quarter note or eighth note. Common time signatures include 4/4, which has four beats per measure and is often used in popular music, and 3/4, which has three beats per measure and is commonly found in waltzes. Understanding time signatures helps musicians maintain rhythm and structure in their performances, making it easier to play together in an ensemble.