Question about Templates

Hi , I was reading a detailed article about templates and I came across the following paragraph

template
class Stack
{
T data[N]; // Fixed capacity is N
size_t count;
public:
void push(const T& t);
};


"You must provide a compile-time constant value for the parameter N when you request an instance of this template, such as Stack myFixedStack;
Because the value of N is known at compile time, the underlying array (data) can be placed on the run time stack instead of on the free store.This can improve runtime performance by avoiding the overhead associated with dynamic memory allocation.

Question:
Now in the above paragraph what does
"This can improve runtime performance by avoiding the overhead associated with dynamic memory allocation." mean ?? What does template over head mean ??
I am a bit puzzled and i would really appreciate it if some one could explain to me what this sentence means thanks...