keystone

Keystone is a term used in architecture and many other fields. In architecture, the keystone is the central wedge-shaped stone at the apex of an arch. The keystone locks the voussoirs into position, allowing the arch to bear weight and transfer loads to the supports.

Beyond architecture, "keystone" is used to describe a keystone species in ecology, a species whose presence maintains the structure of an ecosystem. Its removal can trigger large changes in the community and its function.

Geography and place names include the nickname of Pennsylvania, the Keystone State, reflecting its historical and political significance in early United States history. Towns named Keystone include Keystone, Colorado, a mountain resort, and Keystone, South Dakota, located along the Black Hills region, among others.

In infrastructure, the Keystone Pipeline System is a major oil pipeline network that runs from Canada to the United States and is operated by TC Energy. The Keystone XL project was a proposed expansion that attracted extensive environmental, political, and legal debate.

Overall, the term keystone denotes something that plays a crucial or central role in holding a system together or providing essential support.