What is 'degressive proportionality' system suggested by Tharoor for LS delimitation?

Congress' Shashi Tharoor suggested “degressive proportionality” in Lok Sabha to address southern states’ concerns over delimitation. He said the system, used in European Parliament, has a “minimum threshold” and “maximum ceiling,” with no member state having fewer than six seats or more than 96. Tharoor said it prevents big nations like Germany, France, Italy from holding a permanent majority.