The dispossessed are people who have had property or land taken away — they once had a home, a farm, or a place, and it was taken. Used this way it is often a noun: the dispossessed, meaning that group, not one single verb action. You also meet it as an adjective: a dispossessed family, dispossessed farmers. It is a serious, news-like word. It can cover people pushed off land in war, by the state, or by the rich; the feeling is of loss, of being left with little. It is more specific than poor: the point is that something they had was taken. Though actually, writers like the phrase the dispossessed because it names a whole class of people in two words — kind, but easy to slide past who took the land.