Schadenfreude is a German word. It's hard to translate exactly but the nearest definition is 'taking pleasure in another person's suffering'. It's from the two words 'Schaden' which means harm or damage, and 'Freude' which means joy or pleasure. It's not the same as cruelty or sadism, where you have the idea of actually causing pain or making someone suffer - in Schadenfreude, you don't actually do anything but you enjoy the fact that the other person is suffering. It's often used a bit jokingly - for instance if you enjoy seeing someone else get embarrassed or make a fool of themselves - rather than to suggest enjoyment of serious suffering.
This word is quite often used in English and some other languages. It should be pronounced as in the original German, which is more or less as 'sha-den-FROY-de'. It is one of several German words, like rucksack and hinterland, to have passed into English unchanged.