Well some demographers picked it. If you look at the the birth rates from 46 to 64 you can see they really shot up that entire period and peaking at over 4 million a year until about 1964 when they suddenly fall off a cliff, declining by about 300,000 in one year. From there they fall steadily reaching a low of just over 3 million in 1973. From 46 to 64 the birth rate averaged about 24 births per thousand people. In 1965 that rate drops to 19.4 from 21.7 in 1964. It reaches a low in 1973 of 14.9 per thousand.
Basically it’s used to describe a bubble.
http://www.infoplease.com/ipa/A0005067.html