This summary is not the rule. The rule text controls.
When someone testifies in court, the other side can point out reasons that person might not be telling the whole truth. This rule says you can bring up evidence that a witness has a bias, prejudice, or personal stake in the case. This helps the judge or jury decide how much to trust what the witness says.
For example, if a witness is closely related to one of the parties, works for them, stands to gain money from the outcome, or has a grudge against the other side, that information can come out during the trial. Lawyers often ask questions about these connections when questioning a witness, especially during cross examination.
The point of this rule is to give the judge or jury a full picture of who is testifying and why. A witness might be completely honest, but a jury still deserves to know if that person has a reason to favor one side over the other. It is then up to the jury to decide how much weight to give that witness's testimony.
