Netapp makes storage: primarily, their Data ONTAP series which does network attached and block storage. Since they acquired Engenio, they also sell block-only devices.
NetApp filers are a popular model of network attached storage (NAS) device. NetApp also sell software products catering to the storage reporting and monitoring market niche.
A NetApp filer is a standalone appliance which runs an operating system called ONTAP, and has it's own specialist command set, and is loosely based on BSD. Their primary service offering are for network storage, via CIFS and NFS.
They've also diversified into direct attached storage via iSCSI and FCoE.
Filers are typically configured with a custom variant of RAID-4, that NetApp call RAID-DP. Essentially RAID-4 with a second parity drive.
1 or more RAID groups are turned into an aggregate - a pool of storage.
Volume are created within an aggregate, and may be thin provisioned or deduplicated.*
Qtrees are created within volumes a top level - they're quotaed directory structures. (Enforcing a quota is optional - qtrees merely enable the quota tracking mechanism).
- Filers deduplicate at volume level, because this allows volumes to be treated as standalone containers for the purposes of migration around a cluster.