Grups, a contraction of "grown ups", was the word used by the Onlies, or children, of Earth Two to refer to adults. On that world, adults and children entering puberty developed the fatal form of the life prolongation project. Blue blemishes covered their skin, and they became insane and dangerous. In this state, the adults attacked anyone near them, and destroyed their surroundings.
During the initial outbreak of the plague, three centuries earlier, the children were forced to hide from all adults, including their own parents, until the adults died. This left the children with a deep-rooted fear of and distrust for adults. (TOS: "Miri")
The term "grups" was made up by Gene Roddenberry. He first suggested it in a conversation with "Miri" writer Adrian Spies, in which Roddenberry also proposed that the Onlies have a language of their own. His term for what they would call adults was approved by Spies, who later commented, "I immediately liked it. That's an example of a creative producer at work." (Captains' Logs: The Unauthorized Complete Trek Voyages, p. 31)
On 17 August2006, this term was used in a fashion/culture article in the Vancouver, BC weekly, The Georgia Strait, which stated, "Grups is a recently coined marketing buzzword branding 30- to 50-year-olds who aren't prepared to relinquish their young-at-heartedness. It's lifted from an episode of the old Star Trek TV show set on a planet with no grownups (grups)."