When you hear someone say they are going to "take the fifth" it actually is based upon the Fifth Amendment of the United States Consitution which says every citizen has the right to remain silent and not give testimony against themselves. This is an extremely important distinction between the United States and other countries which do not embrace this concept. In many other places around the world, a Defendant may not remain silent and must explain their position. This same right extends to refusing to say anything to the police if they are questioning a Defendant. That's basically how the Miranda warnings came into being which specifically inform a person who has been arrested that they have the right to remain silent and that anything they say (if they decide to speak) can and will be used against them in a Court of law. This was a major step forward when the Miranda case was written and delivered because it put police all over this country on notice that they could no longer force arrestees to confess by coercing them or forcing them to give them a statement.