Homonym: hum (Melody)
A "hum" is a continuous, low sound that can be produced by various sources, including humans and machines. When people hum, they create a sound by vibrating their vocal cords while keeping their lips closed. This sound can be soothing and is often associated with relaxation or concentration.
In addition to human vocalization, many devices, such as electric motors and refrigerators, can produce a humming noise during operation. This sound is typically a result of mechanical vibrations or electrical currents. Humming can also be a sign of normal functioning or, in some cases, indicate a need for maintenance if it becomes unusually loud.