Privilege against self-incrimination
The privilege against self-incrimination is the right of anyone to refuse to answer questions when the answers might increase the likelihood of criminal incrimination. In other words, no one can be forced to testify against himself.
There are exceptions if a witness is granted use or transactional immunity, such that what he says cannot be used against him (use immunity) or he has received full immunity for any prosecution for the underlying crime or transaction (transactional immunity). If the witness has immunity, then he cannot refuse to answer questions when ordered to do so by a judge.