Definition of: phototaxis

(fō′tō·tak′sis) noun Biol.
The assumption by an organism of a definite position with reference to the direction of the incident ray of light, called negative phototaxis when the movement is away from the light, and positive phototaxis when the movement is toward the light. Also pho′to·tax′y. [<NL <Gk. phōs, phōtos a light + taxis an arrangement]
—pho′to·tac′tic (-tak′tik) adjective
—pho′·to·tac′ti·cal·ly adverb