Self-incrimination is the process of accusing oneself of a crime for which a person can then be prosecuted. Self-incrimination can occur in one of two ways: directly or indirectly. Direct self-incrimination is when a person incriminates themselves during an interrogation procedure. Indirect incrimination is when a person incriminates themselves voluntary and without pressure from another person. Citizens of the United States are protected from self-incriminating themselves under the Fifth Amendment of the Constitution. The Fifth Amendment is part of the Bill of Rights. When people say they are going to "plead the fifth" it means that they are going to enact their Fifth Amendment rights and not say anything that will incriminate them in a situation.
The text of the Fifth Amendment reads:
"No person shall be held to answer for a capital, or otherwise infamous crime, unless on presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia, when in actual service in time of War or public danger; nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; nor shall be compelled in any criminal case to be a witness against himself, nor be deprived of life, liberty, or property, without due process of law; nor shall private property be taken for public use, without just compensation."
The right to protect oneself from self-incrimination arose from the days of torturing prisoners or people that are detained by law enforcement officials. This right gives people the option of not incriminating themselves when being arrested. Suspects that are being arrested are read their Miranda Rights, as defined in the decision of the Supreme Court case of Miranda v. Arizona, and one of the rights read is the right to remain silent. Miranda Rights are read like this:
"You have the right to remain silent. Anything you say can and will be used against you in a court of law. You have the right to have an attorney present during questioning. If you cannot afford an attorney, one will be appointed for you. Do you understand these rights?"
If the suspect being arrested by the officer declines the rights afforded to him or her by the Constitution of the United States then whatever they say can and will be used or held against them in a court of law. This means that whatever the suspect says to the officer or to other people in the vicinity can be documented and presented to the prosecutor or the judge handling the court case.
Along with the ability to not speak to the arresting officer upon arrest is the ability to refuse to testify during a trial. The right to do so is also protected under the Fifth Amendment of the United States Constitution. If a witness takes the witness stand and is sworn in under oath, they do not have to answer any of the questions posed to them by the prosecution or the defense. All they need to say as their answer is "I plead the fifth." It will be recorded by the court reporter that the witness pled the fifth and refused to answer the question. The witness cannot be penalized for not answering questions posed to them while on the stand. The only thing a witness can be penalized for while on the stand is lying about the answers to questions while they are under oath.
The Fifth Amendment does not protect a defendant when it comes to submitting a DNA sample or submitting a finger print test. A defendant cannot plead the fifth when it comes to these two tests. They must be performed and if they are not the defendant can be held in contempt of court.