Garbage Collection is a form of automatic memory management. It is a feature of many modern languages that you may have already used (C#, Python, Javascript, etc.) so you may already be using it without even knowing! In a garbage collected environment objects are automatically removed from memory after you stop using them. This means you can create a new object, use it for a while, and when you are done using it you set the variable that points to it as null and that's the end of your worries. Behind the scene the garbage collector ("GC") is keeping track of what objects are still being used. When an object is no longer being used the garbage collector automatically frees up the memory.
Lower level languages such as C and C++ do not provide a garbage collector out of the box. This means you have to manually keep track of what memory is being used and free it when you no longer wish to use it. This can be bug prone and is harder for a programmer to manage so Unreal Engine 4 has c