@billiardsforum - I have shot pool in league and in various pool tournaments for the past 40 years, and I humbly beg to disagree with the last answer.
Obviously, jumping the cue ball by digging under or scooping the cue ball with the cue's tip below the equator is indeed a foul in eight ball pool as you mentioned above.
The "jump shot" is indeed legal in 8 ball, if done correctly—that is, doing it in such a way that the cue's tip strikes the cue ball at or above it's center line.
However, using a jump cue and elevating the butt end of it so as to hit downward on, and into the cue ball, thereby causing it to jump over an impeding ball is certainly legal.
Here's the definition of "jump shot" from the World Pool-Billiard Association rules, which supports this (emphasis mine).
8.16 Jump Shot (8 Ball)
A jump shot is one in which the cue ball is made to go over an intervening obstacle such as an object ball or part of the cushion. Whether such a shot is legal depends on how it is accomplished and the intention of the shooter. Usually a legal jump shot is played by elevating the cue stick and driving the cue ball down into the playing surface from which it rebounds.
The jump shot is a technique that should be learned and cultivated in the game of eight ball. This is certainly a common shot here in Ohio and surrounding states and I've seen the pros using this shot on TV while playing in tournaments.