What is the difference between kaffarah (expiation) and qadaa' (making up for a missed act of worship), and when do they coincide?

When scholars mention qada' (making up missed fasts) and kaffarah (definition) (expiation) in relation to fasting, qada' refers to fasting the days missed from Ramadan (definition). As for kaffarah, it is of two types: a severe kaffarah for one who intentionally has intercourse during a Ramadan day, and a minor kaffarah for other cases, such as delaying the making up of missed Ramadan fasts without a valid excuse until the next Ramadan begins, or the kaffarah for a nursing or pregnant woman if they break their fast out of fear for the child; in such cases, they must both make up the fasts and offer expiation.