As we know objects are created inside heap memory and Garbage collection is a process which removes dead objects from Java Heap space and returns memory back to Heap in Java. For the sake of Garbage collection Heap is divided into three main regions named as New Generation, Old or Tenured Generation and Perm space. New Generation of Java Heap is part of Java Heap memory where newly created object are stored, During the course of application many objects created and died but those remain live they got moved to Old or Tenured Generation by Java Garbage collector thread on Major or full garbage collection. Perm space of Java Heap is where JVM stores Meta data about classes and methods, String pool and Class level details. You can see How Garbage collection works in Java for more information on Heap in Java and Garbage collection.