Heap memory stores shared objects used by the application. It is not thread safe. 

Stack memory stores references to objects in the heap. It also stores temporary variables used in methods etc. Stack memory automatically releases allocations when methods are finished executing. Stack memory is faster to access than heap memory and is thread safe. 

heap memory relies on garbage collection to free memory for your application. Heap memory is slower to access but has significantly more space than stack memory 

Tech Lead 101

Heap memory stores shared objects used by the application. It is not thread safe.