playground

noun

1. A large open space for children to play in, usually having dedicated play equipment (such as swings and slides).

   “The kids have to go to the playground during recess, no matter the weather.”

   “The local council have set up a new playground, equipped with slides, swings, and a climbing wall.”

   “Where else in the world can you pre-order sushi and fondue on some of the trains, travel in family carriages equipped with mini-playgrounds, or use a request stop button at some small stations? Where else can you hear the announcement: "The train at Platform 4 is ten minutes late due to an incident in another country," as I did once at the Swiss station of Spiez?”

2. (figuratively)Any physical or metaphysical space in which a person or organization has free rein to do as they please.

   “The exclusive tropical island was a millionaire's playground.”

   “Kjelsås (six miles) marks the end of the suburbs, and the line immediately plunges into Nordmarka. This vast untamed area of forest and mountain (much of it over 2,000 ft. above sea level), interspersed with innumerable lakes, large and small, is known as Oslo's playground.”

3. A sandbox for testing calls to an application programming interface.