Cross-examination is the general right for an party adverse in interest in a civil or criminal proceeding to ask questions of a person who has given testimony or made an affidavit. Failure to undergo or co-operate with cross-examination can be grounds for refusing to take testimony or affidavits into evidence.
The general purpose of cross-examination is to point out inconsistencies in the person's testimony, or to get them to make admissions that are against their own interests.
One of the most famous cross-examinations was at the Nuremberg Trials where Sir Hartley Shawcross cross-examined Hermann Goering. Goering had claimed that his actions prior to World War II were the result of civil unrest and not a direct attack against Germany's Jews. Goering had done well when cross-examined by U.S. Supreme Court Justice Robert Jackson, but Shawcross confronted Goering with his own signed documents and spoken statements regarding Germany's Jews, showing that he was fully involved with the seizure of their property and ignored their personal well being.