Plane Breaks Sound Barrier
If a boat travels faster than the waves can propagate through water, then the waves 'can't get out of the way' of the boat fast enough, and they form a wake. A wake is a larger single wave. It is formed out of all the little waves that would have propagated ahead of the boat but could not.When an travels through the air, it produces sound waves. If the plane is traveling slower than the speed of sound (the speed of sound varies, but 700 mph is typical through air), then sound waves can propagate ahead of the plane.
Passenger Plane Breaks Sound Barrier
If the plane breaks the sound barrier and flies faster than the speed of sound, it produces a sonic boom when it flies past. The boom is the 'wake' of the plane's sound waves. All of the sound waves that would have normally propagated ahead of the plane are combined together so at first you hear nothing, and then you hear the boom they create.It is just like being on the shore of a smooth lake when a boat speeds past.
Concorde Plane Breaking Sound Barrier
There is no disturbance in the water as the boat comes by, but eventually a large wave from the wake rolls onto shore. When a plane flies past at supersonic speeds the exact same thing happens, but instead of the large wake wave, you get a sonic boom.For more information on this and related topics, check out the links below.