What is "z.p.g."

Z.P.G. (short for " Zero Population Growth") is a 1972 Danish-American dystopian science fiction film starring Oliver Reed and Geraldine Chaplin and directed by Michael Campus. It is inspired by the non-fiction best-selling book The Population Bomb by Paul R. Ehrlich. The film concerns an overpopulated future Earth, whose world government executes those who violate a 30-year ban on having children. Filmed in Denmark, the film is almost entirely set-bound featuring art direction designed to reflect a bleak, oppressive future.