Voir dire

(French) oath of witness; initial examination of a legal witness in order to determine if he or she is fit to give testimony

Voir dire (IPA ) is a phrase in law which derives from Middle French. In origin it refers to an oath to tell the truth (Latin verum dicĕre), in other words to give a true verdict. The word voir (or voire), in this context, is an old French word meaning "truth". It is unconnected with the modern French word voir, which derives from Latin vidēre ("to see"), though the expression is now often interpreted by false etymology to mean "to see [them] say". In the UK, Australia, New Zealand, and Canada, it refers to a "trial within a trial". A hearing to determine the admissibility of evidence, or the competency of a witness or juror. In the United States, it now generally refers to the process by which prospective jurors are questioned about their backgrounds and potential biases before being invited to sit on a jury. For more detail, see Jury selection.
See more at Wikipedia.org...

voir dire, (French), initial examination of a legal witness in order to determine if he or she is fit to give testimony

An oath administered to a witness, usually before being sworn in chief, requiring him to speak the truth, or make true answers in reference to matters inquired of, to ascertain his competency to give evidence.
  

A mini-hearing held during a trial on the admissibility of contested evidence. - (read more on Voir dire)