Answer:
When an item stands for some sort of meaning such as how a dove might stand for peace.
Step-by-step explanation:
Various items in a story may take on a meaning or use an existing meaning. In the example above, the image of a dove can stand for peace or an eagle for freedom or a chain for bondage. However, in the course of a story, these meanings could change. If someone was in a crisis, and found a dying dove, and tried to save it, and it died when their crisis deepened, then the symbol of the dove might change to something darker. The same is true for the other symbols above.
Sometimes, with literary symbolism, the author may take something that has little or no different or associated meaning in everyday life. The color green, for example, could become a meaningful symbol in a story. A story might revolve around the impact of nature on a city, and the characters note the different varieties of green. Then a tragedy might happen, and the green colors disappear due to some negative event like warfare. Then when the characters recall the color, they do so with a certain wistfulness.