Recursion is a process in which a function or method calls itself directly or indirectly to solve a particular problem by solving smaller subproblems of the original problem. In mathematics and computer science, recursion is used to define a concept or process that depends on a simpler version of itself. A recursive function definition has one or more base cases, which are terminating scenarios that do not use recursion to produce an answer, and one or more recursive cases, which are sets of rules that reduce all successive cases toward the base case). Recursion is a powerful tool in writing algorithms and can be used to solve problems such as tree traversals, Tower of Hanoi, and calculating Fibonacci numbers. However, it can also be inefficient and lead to stack overflows if not used carefully, and can make the code more difficult to understand and debug.