A reflex action, differently known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. Scientific use of the term "reflex" refers to a behavior that is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.
The stretch reflexes (often called deep tendon reflexes, though not to be confused with Golgi tendon reflexes) provide information on the integrity of the central nervous system and peripheral nervous system. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.
While the reflexes above are stimulated mechanically, the term H-reflex refers to the analogous reflex stimulated electrically, and Tonic vibration reflex for those stimulated to vibration.