The idea came from the US labor movement. In the early 1990s, Tony Mazzocchi of the Oil, Chemical and Atomic Workers union called for a "Superfund for workers." People who lost jobs to environmental rules would get income support and education. As he put it in 1993, there was a Superfund for dirt and there ought to be one for workers.
Environmental justice groups widened the concept. Black, Indigenous and Latino communities living next to refineries, mines and power plants argued that a transition is not just if it builds new clean energy in wealthy areas while old pollution stays in theirs.
Today a just transition means job guarantees and retraining, cleanup of contaminated sites, community ownership of new energy projects and a voice for frontline residents in decisions. It is the labor and racial justice side of climate policy.