What information and objects are usually placed in the memory area called the heap?

In the heap, objects and data with unknown size or dynamically changing lifetime are usually placed. In iOS, this includes:

• Class objects (e.g., instances of NSObject and its subclasses).
• Data allocated dynamically via alloc, malloc, etc.

The heap is managed by the memory management system (ARC or manual), and objects live in it as long as there are references to them. Unlike the stack, which stores local variables and function parameters with short lifetimes.