Second derivative is the rate of change of the derivative, i.e "how fast is the gradient changing?".
Say the second derivative is 1 at point A and 2 at point B on the same function. Then the gradient (the derivative) is changing faster at point A than point B.
i guess i already knew this,just did not actually think about it.
However, if this is what i was looking for, i will see later when i think more about it, and if i still have problems i will come back.