A more thorough explanation:

An at-issue waiver is a legal term that refers to an exemption from the attorney-client privilege. This means that a litigant (someone involved in a lawsuit) is considered to have given up their right to keep certain information confidential if they take a position in the case that cannot be effectively challenged without analyzing that confidential information.

For example, let's say that a company is being sued for patent infringement. The company's lawyer has been advising them on how to design their products to avoid infringing on patents. If the company argues in court that their products do not infringe on any patents, they may be considered to have waived their attorney-client privilege regarding the advice they received from their lawyer. This is because the other side cannot effectively challenge the company's position without analyzing the advice from the lawyer.

Another example could be a criminal defendant who claims that they did not have the intent to commit a crime. If the prosecution argues that the defendant did have the intent to commit the crime, the defendant may be considered to have waived their attorney-client privilege regarding any conversations they had with their lawyer about their intent.

Overall, an at-issue waiver is a way for the court to ensure that both sides have access to all relevant information in a case, even if that information would normally be protected by the attorney-client privilege.