Infra sound is sound that is lower than the human hearing range (below 20Hz). It is usually felt as a vibration, due to its low frequency. It can be produced by natural events such as volcanic eruptions, earthquakes, and avalanches, as well as man-made sources such as industrial machinery and explosions.
Ultra sound is sound that is higher than the human hearing range (above 20kHz). It is usually used for medical imaging and diagnostic purposes, such as sonograms and ultrasounds. It can also be used to detect objects underwater, measure distances, and measure the speed of sound in a medium.