In a medical sense, immunity is a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion.
In a legal sense, immunity confers a status on a person or body that makes that person or body free from otherwise legal obligations such as, for example, liability for damages or punishment for criminal acts. Transactional immunity refers to the inability of the prosecutor to prosecute a witness in exchange for the witness's testimony, an action referred to as "turning state's evidence." Under use immunity, the government may not use a witness's grand jury testimony to prosecute that person. But if the state acquires evidence for a crime independent of the testimony, then the witness can be prosecuted.
