Ghost

If an expression, especially a Common subexpression, could have formed a proper abstraction, but is not made into a separate nonterminal, we speak of it as a Ghost. An example of a Ghost could be an omnipresent qualified identifier that is always used as Id ("." Id)*.

Reference

Mats Stijlaart and Vadim Zaytsev. 2017. Towards a taxonomy of grammar smells. In Proceedings of the 10th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2017). ACM, New York, NY, USA, 43-54.