Thigmotropism is the growth response to mechanical stimulation or touch.
Tropism is growth response in all or part of a plant due to an external stimulus. Thigmotropism is in response to touch (thigmo-) and may be further divided as negative or positive thigmotropism.
Negative thigmotropism will cause the plant to move away from the stimulus, while positive thigmotropism will cause the plant to move towards the stimulus.
Thigmotropism is especially valuable in climbing plants which rely on their sense of touch to find and attach to nearby objects.