Tropism is a response to certain stimuli. A positive tropism is moving towards the stimuli, while a negative tropism is moving away from a stimuli.
Positive Phototropism - Growing towards light
Negative Phototropism - Growing away from light
Positive Thigmotropism- Moving towards touch
Negative Thigmotropism- Moving away from touch
Positive Hydrotropism - Growing towards water
Negative Hydrotropism - Growing away from water
Positive Gravitropism - Growing towards ground
Negative Gravitropism - Growing upwards