A more thorough explanation:

Definition: A secondary invention is a new and useful invention that uses or combines existing elements or combinations to achieve a new and useful result.

Example: A smartphone with a built-in heart rate monitor is a secondary invention. The heart rate monitor is not a new invention, but combining it with a smartphone to track fitness is a new and useful result.

Explanation: The example illustrates how a secondary invention can take existing elements or combinations and create something new and useful. In this case, the heart rate monitor and smartphone were already established technologies, but combining them created a new product that can track fitness and health.