However, my simpler definition is that recursion is the following “defining something in terms of itself in some way.” A similar concept to recursion is the Droste effect, where an image contains a smaller sub-image of the larger image. We see recursion in movies like Inception, where a dreamer dreams about dreaming, or in recursive artwork. Recursion can also be used to define infinite shapes like infinitely shrinking circles, rings, and tunnels.
Recursion exists in mathematics as a function defined in terms of itself. An example of a recursive function is the factorial function. This is often notated with an exclamation mark and is defined as the product of all the numbers from 1 to an integer N. We can define the factorial function recursively as the recurrence relation.