A symbol is
A. a comparison using like or as.
B. a tangible object that represents something abstract.
C. a figure that resembles the object it was patterned upon.
D. a reference to something with which the reader is already familiar.
Here the best answer is B. a tangible object that represents something abstract.
Although it does not have to be tangible, ie something you can touch. It can be a representation, for example: A green light is a symbol for "you can go ahead"