What type of meeting occurs when a project manager provides updates to a CEO without prior scheduling?

Ad hoc reporting is the correct choice because it refers to reports or meetings that are not pre-scheduled and occur as needed. In this context, a project manager providing updates to the CEO on the project's status without a prior appointment exemplifies the nature of ad hoc communications. These types of interactions are typically informal, allowing for flexibility in sharing information and addressing concerns as they arise.

External status reporting usually involves sharing project updates with stakeholders outside the immediate project team, which implies a structured or scheduled process. Progress reporting generally refers to regularly scheduled updates that follow a set cadence, ensuring stakeholders receive consistent and timely information. Gap analysis is a different concept altogether, focusing on comparing current performance with desired performance to identify discrepancies. Therefore, ad hoc reporting is the most fitting term for spontaneous communications not bound by a predefined schedule.