A playground at the Historic Bozeman theme park
A playground was a location where children played. Playgrounds, such as the First Contact Fun Zone for example; had swings, slides and other equipment. (LD: "Grounded")
In 2259, there was a playground at the town square on the main street of the colony on Parnassus Beta. (SNW: "Hegemony")
In 2369, Q attempted to lure Amanda Rogers to the Q, saying the whole universe could be her playground. (TNG: "True Q")
In 2372, Kathryn Janeway lamented Naomi Wildman's having been born on USS Voyager in their current predicament, saying Voyager was no more of a nursery than the Delta Quadrant was a playground. (VOY: "Deadlock")
In 2373, Q promised Janeway that were they to have a child together, the whole universe would be their child's playground. (VOY: "The Q and the Grey")