Definition & Meaning of "{not} [be] rocket science"

What is the origin of the idiom "not rocket science" and when to use it?

The idiom "not rocket science" is often used to convey that a task or concept is relatively simple and doesn't require a high level of expertise. The phrase likely comes from the fact that rocket science, or aerospace engineering, is considered one of the most complex and challenging fields. This expression has been a common idiom in English since at least the mid-20th century.