RPO stands for «Recovery Point Objective». This value denotes the maximal permissible age of a functional backup; in other words, RPO shows you how up-to-date your backup is and whether you’d lose critical data if you were to use it. For example, if your last update is from 16 hours ago while your RPO value is at 18, you will not experience significant losses. It is, however, important to keep in mind that this value should be kept as low as possible: while the losses may not be critical to the functioning of your business, it is preferable that less data is lost overall.
RTO means «Recovery Time Objective»; this value sets the timeframe for you to recover your data without critical losses. While RPO tells you how old a backup can be for the data losses to be acceptable, RTO shows you how long it will take before the losses severely impact your business.