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 as a fraction at the beginning of a piece of music, with the top number showing the number of beats per measure and the bottom number indicating the note value that gets one beat, such as quarter note or eighth note. Common time signatures include 4/4, which has four beats per measure, and 3/4, which has three beats per measure. These signatures help musicians understand the rhythm and structure of a piece, guiding them in how to play or conduct the music accurately.