As soon as you start to deal with backup strategies, you will come across two abbreviations you need to deal with: RTO and RPO.
Recovery Time Objective (RTO) simply means the time in minutes until a crashed system is up and running again. For example, if your backup server is able to restore your entire file server within 60 minutes, you have a RTO of 60.
However, this does not say anything about if the data you have restored were from one hour ago, yesterday or from last year. This is defined by the Recovery Point Objective (RPO).
A quick example: You save your file server every night at 20:00 (8pm). One day, all data on this server is lost at 11:00 (11am). You then do the restore and everything is up and running again at 13:00 (1pm).
In this example, you had an Recovery Time Objective (RTO) of 120 minutes (11:00 - 13:00). The Recovery Point Objective (RPO) was however 15 hours (20:00 - 11:00).
Dealing with these values can be quite challenging, but sometimes the biggest problem is not to confuse RTO with RPO.
I simply remember RTO as "Ready to gO" (after a crash) so RPO means how old the backup can be.