Excerpts from Books and Wikipedia
[Cambridge Illustrated History of Warfare, p. 380] "A ballistic missile is a missile only guided during the relatively brief initial powered phase of flight, whose trajectory is subsequently governed by the laws of classical mechanics, in contrast (for example) to a cruise missile which is aerodynamically guided in powered flight." [Wikipedia]
In 1974, the U.S. had 1,054 and the USSR 1,575 ICBs. [Kennedy: Great Powers, p. 395]