Elastic Block Store - AWS persistent storage that attaches to EC2 instances. Like having a dedicated hard drive that you can unplug from one computer and plug into another.
A database server uses EBS volumes to store data that persists even if the server needs to be replaced.
All are persistent block storage volumes you attach to virtual machines for low-latency disk I/O. They support snapshots/backups and can be detached and reattached to other instances (within platform-specific limits).