The Miranda Warning

The Constitution reserves many rights for those suspected of crime. One of the fears of the Framers was that the government could act however it wished by simply saying an individual was a suspected criminal. Many of the rights in the Constitution and the Bill of Rights, such as habeas corpus, the right to remain silent, and the right to an attorney, are designed to ensure that those accused of a crime are assured of those rights.
Police were able to take advantage of the fact that not everyone knows their rights by heart. In fact, it is likely that most citizens could name a few of their rights as accused criminals, but not all of them. The police's position was that if the accused, for example, spoke about a crime without knowing that they did not need to, that it was the person's fault for not invoking that right, even if they did not know, or did not remember, that they had that right.
This was the crux of the issue in Miranda v Arizona. In 1963, Ernesto Miranda was accused of kidnapping and raping an 18-year-old, mildly retarded woman. He was brought in for questioning, and confessed to the crime. He was not told that he did not have to speak or that he could have a lawyer present. At trial, Miranda's lawyer tried to get the confession thrown out, but the motion was denied. In 1966, the case came in front of the Supreme Court. The Court ruled that the statements made to the police could not be used as evidence, since Miranda had not been advised of his rights.
Since then, before any pertinent questioning of a suspect is done, the police have been required to recite the Miranda warning. The statement, reproduced below, exists in several forms, but all have the key elements: the right to remain silent and the right to an attorney. These are also often referred to as the "Miranda rights." When you have been read your rights, you are said to have been "Mirandized."
Note that one need not be Mirandized to be arrested. There is a difference between being arrested and being questioned. Also, basic questions, such as name, address, and Social Security number do not need to be covered by a Miranda warning. The police also need not Mirandize someone who is not a suspect in a crime.