A more thorough explanation:

A rebuttal witness is someone who is called to testify in court in order to contradict or disprove the testimony of a witness called by the opposing party. This witness is called to provide evidence that contradicts or challenges the testimony of the opposing party's witness.

For example, if a witness for the prosecution testifies that they saw the defendant at the scene of the crime, the defense may call a rebuttal witness who can testify that they saw the defendant somewhere else at the time of the crime. This rebuttal witness is called to contradict the testimony of the prosecution's witness.

Another example could be in a civil case where a plaintiff's witness testifies that they were injured due to the defendant's negligence. The defendant may call a rebuttal witness who can testify that the plaintiff's injuries were not caused by the defendant's actions, but rather by something else. This rebuttal witness is called to disprove the testimony of the plaintiff's witness.

These examples illustrate how a rebuttal witness is used to challenge or contradict the testimony of a witness called by the opposing party. The rebuttal witness is an important part of the legal process as they help to ensure that all evidence is thoroughly examined and considered before a verdict is reached.