Whenever a pool ball is struck with any degree of english, and with a
cue that is not perfectly level, a curve results. In the two
immediately preceding sections, intentional curves of lesser and
greater degrees were described. However, because in most billiards
shots, the cue is slightly elevated, if english is employed, an unintentional (and imperceptible to the naked eye) curve results. This is known as "swerve"
or "the swerve effect". The farther away an intended target is from the
cue ball's original shooting position, the more swerve of the cue ball
will affect where the cue ball arrives. For this reason, use of english
(and unintentional english) are complicating factors in billiards and
swerve must be compensated for. The swerve effect should not be confused with a "swerve shot", previously defined as Commonwealth terminology for a curve shot.