Pillarisation (Dutch: verzuiling) is the politico-denominational segregation of a society. These societies were (and in some areas, still are) “vertically” divided into several segments or “pillars” (zuilen, singular zuil) according to different religions or ideologies. The best-known examples of this are the Dutch and Belgian ones.
These pillars all have their own social institutions: their own newspapers, broadcasting organizations, political parties, trade unions and farmers’ associations, banks, schools, hospitals, universities, Scouting organizations and sports clubs. Some companies even hire only personnel of a specific religion or ideology. This leads to a situation where many people have no personal contact with people from another pillar.
Austrian, Iraqi Arab, Israeli, Lebanese, Maltese, Nigerian, Northern Irish, and Scottish societies may also be considered to have had displayed aspects of pillarisation, historically or in the present time.
Israel is not an apartheid, but it is pillarized by religion, and by religious subgroups, to a degree. Good or bad, black or white, call each thing by its proper name!
I reckon inaccurate “apartheid” was chosen not as a slur, but because the correct definition is unfamiliar: Pillarization.