Recursion is when a function calls itself and is used mostly when it makes the solution cleaner or gives better performance and many algorithms use it for those purposes.

When you write a recursive function it is important to remember that it will keep calling itself indefinetly. For that reason, the function needs an exit condition which tells it when to stop or you get an infinite loop.

Recursive functions make use of the call stack. A stack is a data structure where you “push” items on top and “pop” the top most item. Computers use internally a “call stack”. Each time a function is executed it gets pushed on to the call stack. In recursion, the self calling functions are in a partially completed state until the recursion finds the exit condiction and each function returns which in turn pops each execution from the stack.

The power of recursion is that we don’t need to keep track of the calls since the call stack takes care of it for us.

Reference book Grokking Algorithms