Data backup
In one sentenceKeeping regular copies of the system's data in a separate place, to restore them if the computer fails, the data is deleted or a virus hits it.
Simply put
Years of journal entries and invoices can be lost to a disk failure or ransomware. Backup is your only insurance against that.
Make it automatic and regular, keep a copy outside the business premises or in the cloud, and test restoring from time to time; a backup that has never been tested may not work when you need it.
Example
On Sunday morning an accountant finds that the server has failed. Because the business keeps a copy in the cloud every night, the system is restored on another computer with Saturday evening's data, and only what was recorded on Sunday morning before the failure has to be re-entered.
Don't confuse it with
Cloud-based systemWorking in the cloud does not on its own replace backup; ask the provider about its policy and how often it backs up.