What is the meaning of Chemical_symbol?

The 1- to 3-letter international code for a chemical element. It is the same in all languages. Thus, gold always has the chemical symbol "Au", regardless of what people call it in their language.

a similar symbol used to denote a different chemical entity, such as an isotope (e.g. D = deuterium, though "H" is more correct), a radical (e.g. Ph [or Φ] = phenyl), an unknown (e.g. M = a metal, or X = a halogen), etc.

Source: wiktionary.org