An invention is something that is made by human beings and that did not exist in the world before. Inventions include items, devices, processes, materials, machines, and toys from AstroTurf® to zippers. A discovery is something that existed before, but was not yet known or “discovered”; for example, the concept of black holes in outer space. Inventions and discoveries usually come about by bringing together existing technologies in a new way, and they may take centuries to take shape. They usually are created in response to a specific human need, such as a medicine to heal sickness; as a result of the creator’s desire to complete a task more efficiently or effectively, such as a tool or machine; or even by accident, such as the Slinky. Sometimes just one person makes the discovery or invention; other times the end result is the product of a team effort. Sometimes different people have made the same invention independently at the same time. In very rare cases different people have made the same invention on the same day.