A strait is either formed by tectonic shifts or land that has subsided or been eroded. If a strait is created by people rather than geological forces, it is generally referred to as a canal.
When straits are created by tectonic shifts, landmasses are pulled apart and a crack appears in an isthmus, a small strip of land separating two bodies of water. When the isthmus cracks, water flows in from each side, creating a strait. Tectonic shifts can also close straits over time, like the strait of Gibraltar where shifting tectonic plates are slowly closing the link between the Mediterranean Sea and the Atlantic Ocean.
Straits can also be formed when land subsides or is eroded - it is slowly removed, and the water flows over the land to create the strait. Straits have historically held great significance because of their impact on travel and transportation of goods.
The Strait of Magellan offered travelers sailing around the bottom of South America both a navigational challenge and a preferable alternative route to the stormy seas of the Arctic region. Other straits, like the Strait of Hormuz which connects the Persian Gulf and the Arabian Sea, offer important economic opportunities because of the trade routes they make possible.