"Uncle Tom" is a name sometimes used to describe Black people who are seen as too complacent or submissive towards white people. It comes from a character in a book called "Uncle Tom's Cabin" who was a slave who was very obedient to his white master. It's not a nice thing to call someone because it implies that they are willing to betray their own people for the benefit of white people. It's important to treat everyone with respect and not use hurtful words like "Uncle Tom."