A destructor is a special member function in object-oriented programming that is automatically called when an object goes out of scope or is deleted. Its primary purpose is to free up resources that the object may have acquired during its lifetime, such as memory or file handles. This helps prevent memory leaks and ensures that resources are properly released. In languages like C++ and Java, destructors are defined with a specific syntax. In C++, a destructor is prefixed with a tilde (~) and has the same name as the class. In Java, the garbage collector handles resource cleanup, but developers can implement finalizers to perform similar tasks, although their use is generally discouraged.