Sounding is an old nautical term meaning "to measure something". You may have heard/read the expression "sound the depths", describing the process of seeing how

Sounding is an old nautical term meaning "to measure something". You may have heard/read the expression "sound the depths", describing the process of seeing how deep the water under the keel of a sailing vessel is. That's the origin of the term. Sounding rockets are rockets launched for scientific research purposes. NASA has the most robust Sounding Rocket program, but there are others out there. Your typical NASA sounding rocket has two or three motor stages and can send a ~1000 lb payload to an altitude of about 280 miles, with about 10 minutes of time above 62 miles (the official demarcation between 99.99% of Earth's atmosphere and space). These are not orbital missions -- you go up and you come back down in the space of 20 to 30 minutes or so. Science objectives include things like observing comets, the composition of the interstellar medium, the dynamics of the Sun, trying to find direct evidence of dark matter, understanding the dynamics of the ionosphere, wind currents in the upper levels of the atmosphere, and many more. For only $1 - $6 million USD per mission, a sounding rocket is a relatively cheap way to do some science in space, and the science payoffs have been huge.