Cavitation - noun. A pocket or cavity created by a flowing liquid or the rapid formation and collapse of vapour pockets within a flowing liquid. Cavitation is a problem for mechanical equipment. The word was accidentally suggested to me by my husband after he watched a documentary about the Three Mile Island disaster and I said, "Cav-i-what-now?" as he described it. You have probably seen this phenomenom in action but didn't know there was a name for it, of course!