A diatonic harmonica is a small, handheld musical instrument that produces sound by drawing air through holes that contain metal reeds. Each hole corresponds to a specific note, and the harmonica is typically tuned to a particular key, making it ideal for playing melodies and simple chords. It is commonly used in genres like blues, folk, and rock. The diatonic harmonica usually has 10 holes, allowing for a range of notes within its key. Players can create different sounds by bending notes, which involves altering the airflow and pitch. This technique adds expressiveness and depth to the music, making the diatonic harmonica a popular choice for both beginners and experienced musicians.