Uncle Tom is a derogatory term for a black person who cooperates with white people or protests injustice mildly instead of violently, or who is otherwise perceived to act in a servile and insincere way around white people. The term Uncle Tom comes from the title character of Harriet Beecher Stowe's novel Uncle Tom's Cabin.
The character of Uncle Tom has dignity in the book, he is strong and capable, but forgiving. It was his servile depiction in the popular stage version that was greatly influential in the development of the epithet. White-haired, shuffling Uncle Tom is supposedly grateful to his master.
Essentially, an accusation of being an Uncle Tom or Tomming questions the accused person's integrity; the implication is that the person is demeaning him- or herself for uncertain benefit and should learn that African-Americans should not be grateful simply for being treated the way people should expect to be treated, but should instead be confident, independent, and self-sufficient, even if this at times provokes a confrontation.
Some blacks labeled with the term have objected on the grounds that it creates a false dichotomy between being polite or being loyal to their race. These advocates say that maintaining good relations is a value in itself and need not necessarily take a back seat to social advancement. Often, the imputed Uncle Tom attitude is said to be a defense of private autonomy in the face of social prejudice, or even as an over the top, satirical response to prejudice. Tomming is seen as a way of preventing maltreatment from whites.
Sometimes women who Tom are called Aunt Jemima after the popular pancake mix that long depicted a kerchief-headed family cook of that name.
Similar views, pro and con, adhere to the expression acting white. Another term along the same lines is Oreo, from the chocolate sandwich cookie with white filling (implying that one is black on the outside but white on the inside).