A sine wave or sinusoid is a mathematical curve that describes a smooth periodic oscillation. A sine wave is a continuous wave. It is named after the function sine, of which it is the graph. It occurs often in pure and applied mathematics, as well as physics, engineering, signal processing and many other fields. Wikipedia

I will always remember the first time I saw an oscilloscope, I may have been 9 or 10. My older cousin who was leaving soon to enter astronaut training led me up to his converted attic/laboratory where he worked with all kinds of scientific apparatus. He turned on the oscilloscope and proceeded to explain how I could actually “see” sound represented in the waves moving across the tiny screen, and how the amplitude and peaks and valleys would change as he dialed up different sounds.