A more thorough explanation:

An examiner's answer is a document filed by a patent examiner in response to an appeal brief filed by an applicant. The examiner's answer is filed with the Board of Patent Appeals and Interferences and is used to defend the examiner's decision to reject the patent application. The purpose of the examiner's answer is to rebut the arguments made in the appeal brief and to provide additional support for the examiner's decision.

An applicant files a patent application, but the examiner rejects the application. The applicant files an appeal brief arguing that the examiner's decision was incorrect. The examiner then files an examiner's answer, which provides a detailed response to the arguments made in the appeal brief and defends the examiner's decision to reject the application.

Another example could be an applicant filing a patent application for a new type of computer software. The examiner rejects the application, stating that the software is not novel or non-obvious. The applicant files an appeal brief arguing that the software is indeed novel and non-obvious. The examiner then files an examiner's answer, which provides a detailed response to the arguments made in the appeal brief and defends the examiner's decision to reject the application.

These examples illustrate how an examiner's answer is used in the patent application process to defend the examiner's decision to reject an application and to respond to arguments made by the applicant in an appeal brief.