The recovery point objective is the maximum acceptable age of the data you restore. An RPO of four hours means backups must run at least every four hours. The recovery time objective is how long the business can tolerate a system being down before the impact is unacceptable.
Setting RPO and RTO per system turns vague hopes into specific requirements for backups, redundancy, and runbooks. A tax practice might set tight targets for its portal during filing season and looser ones for its archive.