What do infrasonic waves typically refer to in terms of frequency?

Infrasonic waves are sound waves that have frequencies below the threshold of human hearing, which is typically around 20 Hz. This means that infrasonic waves are characterized by frequencies that are lower than 20 Hz. These types of waves are used in various applications, including studying natural phenomena such as earthquakes and volcanic activity, as well as in certain medical imaging techniques. The correct understanding of infrasonic waves is pivotal because it distinguishes them from other sound types, such as audible sounds and ultrasonic waves, which have frequencies higher than 20 kHz.