This has been a heavily debated question!
Some claim that “Deflection” refers to the shaft bending out of the way of the cue ball just after impact. Still others use the term to describe what the cue ball does after impact on an off center hit.
Many use the term “Squirt” to describe the cue balls path.
At OB, we refer to what the cue ball does as “Cue Ball Deflection”. We don’t typically refer to what the shaft does after impact as the ball has already left the tip and there is nothing that anyone can do about where it is going at this point.