Wow is also a term used in the field of audio equipment. Ever seen those old spaghetti westerns? They seem to be ok untill you hear the soundtrack, a terrible whining sound is heard instead of a nice violin orchestra, it sounds like and orchestra but somehow it's completely garbled and way out of tune. This is what is called wow in audio-lingo.
Wow is a slow fluctuation in pitch due to mechanical faults in analog recording or reproducing equipment. The rate of wow is usually in the range of 1-5 Hz. With sustained or slow moving sounds (like a violin orchestra), wow can be detected as a slow oscillation of pitch when the frequency variation is about 0.25%. Shorter sounds (like speech) can only be detected at much higher levels of frequency variation.