What is a tropism

Tropism is directional growthPhototropism is directional growth in response to light.Negative phototropism is growing away from the light e.g. in the rootsPositive phototropism is growing towards the light e.g. in the stem
Geotropism is directional growth in response to gravity or the earthpositive geotropism is growing in the direction of gravity e.g. in the rootsnegative geotropsim is growing in against gravity e.g. in the stem