Supersonic speed is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects travelling in dry air of a temperature of 20 °C (68 °F) this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h.
A sonic boom is the sound associated with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion. So that means that the sound source (in this case an airplane), will pass by a stationary observer (like yourself) before they actually hear the sound it creates.
You will find a gallery of incredibly fast and expensive airplanes breaking the sound barrier and thus travelling at supersonic speeds. That means they are going faster than 343 meters per second (1,125 ft per second). To enhance the gallery, just try and imagine the sound that would (eventually) accompany such a sighting. The vapor trails and moisture that appear around the airplanes also add a great touch to these amazing photos. Enjoy!