Backup and replication are two distinct concepts that serve different purposes. Replication ensures the availability of data by maintaining a redundant copy of the database across multiple nodes, allowing for immediate failover in case of node failure. On the other hand, backup provides protection against disasters, such as catastrophic failures or human error, by creating a snapshot of the system at a past moment in time that can be restored to recover lost data. While replication is crucial for maintaining availability, backups are necessary to mitigate the risks associated with less predictable events, making both concepts essential for a robust disaster recovery strategy.