In IR spectroscopy, a type of vibration that generally produces a signal in the diagnostic region of an IR spectrum.
Stretching vibrations change bond lengths. Bending vibrations change bond angles. A stretching vibration changes the bond length. There are two types of stretching vibrations. In symmetric stretching, two or more bonds vibrate in and out together. In asymmetric stretching, some bonds are getting shorter at the same time as others are getting longer.