pseudoelement

Noun

 * 1)  An object in code that behaves like an HTML element but is not a true element.
 * 2) In a chemical formula, something that is called by a chemical symbol, but is not an element; e.g. Et may mean ethyl group, or Ph (or Φ) may mean phenyl group. (See "" on Wikipedia; said article has a subsection titled "Pseudoelement symbols".)