n. An act of irradiating, or state of being irradiated.n. illumination; irradiance; brilliance.n. figurative: mental light or illumination.n. the apparent enlargement of a bright object seen upon a dark ground, due to the fact that the portions of the retina around the image are stimulated by the intense light; as when a dark spot on a white ground appears smaller, or a white spot on a dark ground larger, than it really is, especially when a little out of focus.n. a process of sterilisation whereby radiation is passed through a bag containing food, utensils, etc., to sterilise the contents.