The story
From red + geyser. Coined in 2016 by the research team at the SDSS-MaNGA Survey; from being a red galaxy with a galactic nucleus fountaining in its center.
Etymology from Wiktionary, CC BY-SA 4.0.
red geyser
Today it means: A galaxy which has stopped star formation due to the energetic winds spewing forth from the active galactic nucleus, heating and disrupting gas accumulation and collapse to form new stars, resulting in a population of aging reddening stars. Full definition →