A glass ceiling in an organisation is an unofficially bar to the promotion of certain types of staff, normally women. It is called glass because its not obviously there, but it is in fact.
A glass escalator is an unofficial fast track promotion of certain types of staff, usually men, within an organisation. This is typical in female dominated organisations where men seem to have preferment.
Glass walls presumably prevent the sidewards movement of one type of staff whilst other types have no problem.