An eighth note is a musical note that lasts for half the duration of a quarter note. It is represented by a filled-in oval note head with a straight stem and one flag. In sheet music, eighth notes are often grouped together, making it easier to read and play faster rhythms. In a standard time signature like 4/4, there are eight eighth notes in one measure. Musicians often use eighth notes to create a lively and energetic feel in their compositions. They are essential for adding rhythmic variety and complexity to music across various genres.