The upper class is the group of people at the top of a society — the ones with the most money, land, or inherited position. As a noun it usually comes with 'the': 'the upper class', or 'the upper classes' when you are thinking of it as several layers. As an adjective it takes a hyphen: an upper-class family, an upper-class accent, upper-class habits. In Britain, where this word is used most, it does not mean simply rich. It carries the old idea of family and birth — someone can be very wealthy and still not upper-class, because their grandparents were not, and someone can be short of money and still be upper-class because of the family they come from. That is why British people talk so much about an upper-class accent or upper-class schools: those are the signs the word is really tracking. The usual set is working class, middle class, upper class, with 'upper-middle-class' sitting in between and doing a lot of work in real conversation. The word can sound neutral in a sociology book and slightly sharp in a conversation, depending on the speaker — used about someone, it can quietly mean 'and they look down on us'.