Use forms as a customary representation of concepts.
Symbolism (symbol on), a term originated from Greek Symbolon, originally meant as a token of "a piece of wood (or a piece of pottery) is divided into two halves, the host and the guest each hold one, and put it together when they meet again to show friendship".
After several evolutions, its meaning has changed into "using a form as a habitual expression of a concept", that is, it is extended to express any idea or thing, and any symbol or object that can express some idea or thing is called "symbol". It is different from the metaphor that people usually use. It involves the essence of things, and its meaning is far broader than metaphor. It is an artistic trend of thought that appeared in Britain and several western countries at the end of 19.