What is the difference between Thread Local Area (TLA) and Thread Stack Size (Xss)?
As the definition says the Thread Local Area is a portion of the heap where each thread can allocate objects. All threads access the same heap: Thread 1 can access objects created by Thread 2 and vice-versa; TLA separates the heap only for object allocation: each thread can only allocate objects in that area, but can access any object in the heap.
The thread stack is a portion of the stack; each thread has its own stack and the thread stack size mentions the size of the stack. A thread cannot access the stack of other threads.
TLAs are part of the heap. Stacks are not on the heap.
See this other question if you don't understand the difference between stack and heap.