A symbol is something that is used for or regarded as representing something else. It may be a material object which represents an abstract or immaterial entity or idea such as a fish or cross to represent Christianity. The use of symbols in a figurative sense is known as symbolism.
In written form, a symbol can be a single character, letter, number, shape or a combination of several of these to designate something. In mathematics the algebraic symbols x and y represent unknown or variable quantities. In chemistry the elements are assigned one ot two-letter symbols such as He for helium. In financial markets stocks, bonds, mutual funds etc. are are given symbols comprising a small series of letters. Generally the fewer letters that a financial instrument has then the more important and widely traded it is.