Often referred to by the acronym JBOD, Just a Bunch of Disks isnt really a standard, more like a (bad) practice.
A JBOD is an array of hard disks that haven't been set up in a proper RAID configuration. Under Linux, a JBOD will look like this:
/dev/hda1 -> /
/dev/hdb1 -> /mnt/hdb
/dev/hdc1 -> /mnt/hdc
/dev/hdd1 -> /mnt/hdd
/dev/hde1 -> /mnt/hde
You get the picture. Sometimes all the directories under each drive will be symlinked to a single location (eg /store), and that directory can than be shared via NFS, SAMBA or whatever tickles your fancy.
This configuration is typically seen on warez servers whos admins want to get the most bang for their buck when it comes to hard disks. In a JBOD configuration every last bit can be used on each drive. Unlike RAID-0 or Linear Append configurations if a JBOD loses a disk then only the data on that disk is lost, rather than the entire 'array'. The disadvantage is, of course, there is no redundancy. JBOD configurations are unfortunately common in many back office servers and rely on tape (often DDS-3 or DAT) for redundancy.
In an environment where your data is worth more to you than the cost of a hard disk, RAID-5 is a far better option for peace of mind and can be implemented for the cost of a redundant drive.
JBOD as a 'technology' is creeping into the SAN market as vendors emphasise storage space and speed over redundancy . Adaptec and RAIDCore both use the acronym in their copy as a 'feature' for their RAID controllers.