Glass ceiling
A glass ceiling is an idea that people use to talk about why some people do not get promotions in companies, schools, and other groups.  A company has a glass ceiling if it looks as if women and minorities could become leaders but they never really do.  That is called a glass ceiling because a new employee starting at the bottom (the "ground floor"), can see all the way up to the top of the building (leadership), but really there is a barrier in the way.