A more thorough explanation:

Definition: Bias refers to a pre-existing inclination or prejudice for or against someone or something. In criminal law, bias is used to describe a situation where a witness may unconsciously or otherwise give testimony in favor of or against a party due to their relationship with that party.

Example: In the case of United States v. Slough, a witness was found to have a bias towards the defendant due to their personal relationship. This bias may have influenced the witness's testimony, leading them to give evidence that was favorable to the defendant.

Explanation: This example illustrates how bias can impact the reliability of witness testimony in criminal cases. When a witness has a bias towards a party, they may be more likely to give evidence that supports that party's case, even if it is not entirely truthful. This can make it difficult for judges and juries to determine the facts of a case and can lead to wrongful convictions or acquittals.