Definition from Nolo’s Plain-English Law Dictionary  At trial,
the opportunity to question any witness who testifies on behalf
of any other party to the lawsuit (in civil cases) or for the
prosecution or other codefendants (in criminal cases). The
opportunity to cross-examine usually occurs as soon as a witness
completes his or her initial testimony, called direct testimony.
Cross-examiners attempt to get the witness to say something
helpful to their side, or to cast doubt on the witness's
testimony by eliciting something that reduces the witness's
credibility -- for example, that the witness's eyesight is so
poor that she may not have seen an event clearly. When a
witness's direct testimony ends up being hostile to the party
that called the witness, sometimes that party's lawyer is
allowed to cross-examine his own witness.  Definition provided
by Nolo’s Plain-English Law Dictionary.