A more thorough explanation:

An office action is a communication from a patent examiner to a patent applicant. It is usually sent to explain why the application has been denied. The United States Patent and Trademark Office (USPTO) sends office actions to applicants to inform them of any issues with their patent application.

• First Office Action: This is the initial reply from a patent examiner to a patent application. If the examiner rejects most or all of the claims, it is called a "shotgun rejection." The applicant must respond to the examiner's reasons for rejection, amend the claims, or both.
• Final Office Action: This is a patent examiner's determination that an application is not allowable. The applicant can file a continuation application, appeal the decision, or request continued prosecution.
• Advisory Office Action: This is an office action in which the patent examiner replies to an applicant's response following final rejection of the application. An advisory action addresses the status of an amendment made in the applicant's response to the final rejection, indicates the status of the claims for appeal, addresses an affidavit or exhibit, or responds to a request for reconsideration.

For example, if a patent application is rejected because it lacks novelty or is obvious, the patent examiner will send an office action to the applicant explaining the reasons for the rejection. The applicant can then respond to the office action by amending the claims or providing additional evidence to support the patentability of the invention.

Another example is if the patent examiner finds that the application does not meet the requirements for patentability, such as being too broad or not being sufficiently described. In this case, the examiner will send an office action to the applicant explaining the reasons for the rejection and giving the applicant an opportunity to respond.

These examples illustrate how office actions are used to communicate with patent applicants and ensure that patent applications meet the requirements for patentability.