RTO stands for Recovery Time Objective, which is a metric that measures the maximum acceptable amount of time that an application or a service can be offline or unavailable after a disruption, such as a server failure, a power outage, or a natural disaster. RTO is a key indicator of the disaster recovery capabilities and objectives of an organization, as it reflects the level of tolerance or impact of downtime on the business operations, reputation, and revenue. RTO is usually expressed in hours, minutes, or seconds, and it can vary depending on the criticality and priority of the application or the service. RTO can help an organization to determine the optimal level of backup, redundancy, and recovery for the application or the service, as well as the potential costs and risks of downtime. RTO can also help the organization to choose the appropriate cloud service model, provider, and deployment option that can meet the disaster recovery requirements and expectations of the organization and its customers12

Therefore, the best explanation of the concept of RTOs for restoring servers to operational use is to reduce the amount of time a particular server is unavailable and offline, as this implies thegoal of minimizing the duration and frequency of downtime, and restoring the normal operations and functionality of the server as quickly as possible.