[Sammy O'Neill: ...wondering if any ppl from across the pond could explain what taking the 5th meant? Some part of ur constitution law thing?]
Quite right, Sammy.
The Fifth refers to the Fifth Amendment to the Constitution. Part of the first 10 Amendments which are commonly called The Bill of Rights.
Specifically, the Fifth Amendment says that we have a right not to incriminate ourselves. It means that we cannot be forced to answer questions that might indicate that we have broken the law and the courts are not allowed to assume what our answer would be.
It has several other parts, such as you can't be tried for the same crime twice (double jeopardy) and the government can't talk your property without paying you. But "taking the Fifth" usually refers to self-incrimination.
Of course, as a practical matter, if you are asked, for instance, "Did you kill that guy?" and you answer, "On the advice of my attorney, I am refusing to answer in accordance with my rights under the Fifth Amendment.", then everyone is going to assume that you did it. BUT the court is not allowed to make that assumption and it is basically considered a non-answer to the question. The prosecuter will have to find another way to prove that you did it.
In popular slang the phrase is abbreviated to "taking the Fifth", which used to be a popular saying with mobsters and now is becoming increasing popular with CEOs.