A vision was the mystical experience of seeing from a different perspective.
The Bajoran Prophets and Pah-wraiths often induced visions in those whom they wished to contact. (DS9: "Emissary", "The Reckoning", "Image in the Sand", "'Til Death Do Us Part", "The Circle", and more)
Leading up to USS Voyager's encounter with Species 8472, Kes experienced telepathic visions. As time progressed, her telepathic visions began to increase in both frequency and intensity, each time a vision occurred, specific regions of her cerebral cortex would go into a state of hyper-stimulation, affecting memory engrams and perceptual centers. (VOY: "Scorpion")