At a speed of about 767 miles per hour, depending on temperature and humidity, a moving object will break the sound barrier.
It was not until World War II, when aircraft started to reach the limits of the sound barrier - although without successfully breaking the barrier into supersonic speed - that the term came into use. Now, More than 70 years later, military aircraft can routinely break through the barrier and travel at incredible speeds.
The pictures below demonstrate the still amazing visual effects that occur as military aircraft punch through the sound barrier and travel faster than sound itself.