Heap and Stack in brief

heap (n)
1. An area of memory used for dynamic memory
allocation where blocks of memory are allocated and freed in
an arbitrary order and the pattern of allocation and size of
blocks is not known until run time. Typically, a program
has one heap which it may use for several different purposes.

and

stack (n):
Computer Science. A section of memory and its associated registers used for temporary storage of information in which the item most recently stored is the first to be retrieved.