Frequency is the number of times per second (cycles per second) that a molecule of air bounces (oscillates) back and forth.
Frequency and Pitch: What happens when I speak? Does my vocal fold hit a molecule of air to send it rebounding off the back of my throat, ricocheting around my mouth a few times, and then hurdling out across the room until it strikes someone's ear?
Fortunately, for good hygiene, the answer is no. The action of the molecule is more like that of domino. You‰ve heard of the "domino effect." This is where they line up a row of many dominos.
When one is pushed over, it knocks the next one over in line, and so forth. You can watch the energy propagate itself along the line, although no domino moves farther then its length.
There is one big difference. The domino just lies there, whereas a molecule of air bounces back like a ping pong ball. If the vocal folds are still moving, the molecule gets whacked repeatedly and bounces back again, and again and again.
Count the number of times this happens each second and you have what is called, the frequency.