The bass drum is a large drum that produces a note of low definite or indefinite pitch. The instrument is typically cylindrical, with the drum's diameter much greater than the drum's depth, with a struck head at both ends of the cylinder. The heads may be made of calfskin or plastic and there is normally a means of adjusting the tension either by threaded taps or by strings. Bass drums are built in a variety of sizes, but size does not dictate the volume produced by the drum. The pitch and the sound can vary much with different sizes, but the size is also chosen based on convenience and aesthetics. Bass drums are percussion instruments and vary in size and are used in several musical genres. Three major types of bass drums can be distinguished.

• The type usually seen or heard in orchestral, ensemble or concert band music is the orchestral, or concert bass drum (in Italian: gran cassa, gran tamburo). It is the largest drum of the orchestra.
• The kick drum, a term for a bass drum associated with a drum kit, which is much smaller than the above-mentioned bass drum. It is struck with a beater attached to a pedal, usually seen on drum kits.
• The pitched bass drum, generally used in marching bands and drum corps, is tuned to a specific pitch and is usually played in a set of three to six drums.

In many forms of music, the bass drum is used to mark or keep time. The bass drum makes a low, boom sound when the mallet hits the drumhead. In marches, it is used to project tempo (marching bands historically march to the beat of the bass). A basic beat for rock and roll has the bass drum played on the first and third beats of bars in common time, with the snare drum on the second and fourth beats, called backbeats. In jazz, the bass drum can vary from almost entirely being a timekeeping medium to being a melodic voice in conjunction with the other parts of the set.