What is prarabdha karma and sanchita karma?

Sri Sri Ravi Shankar: Some karma can be changed and some cannot. When you prepare halwa, if sugar is less or ghee is less, water more or less, it can all be adjusted. But once sooji (a type of flour) is cooked, it cannot be reversed. If the buttermilk is sour, milk can be added, salt can be added to make it drinkable. But it can never be reversed back to milk. Prarabdha karma cannot be changed. Sanchita karma can be changed by spiritual practices.