RPO stands for Recovery Point Objective. The RPO is how much data you can afford to lose in the event of a disaster. RPO is usually measured in units of time. RPO is depicted as the age of the backups you can afford to restore at the point of a disaster. RPO therefore reflects the frequency of backups required.
For example, if you have a RPO of 5 hours, your business can afford to lose up to 5 hours worth of data in the event of a disaster. You must therefore run backups at least every 5 hours in order to meet your RPO.
As with RTO, RPO will need to be negotiated and decided by the business to form an SLA. Specifically the service stakeholder.