LVM2 refers to the userspace toolset that provide logical volume management facilities on linux. It is reasonably backwards-compatible with the original LVM toolset.
Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel. Most modern Linux distributions are LVM-aware to the point of being able to have their root file systems on a logical volume.
Introduced 18 November 2002, LVM2 provides a new format and toolset that provides advanced features while still being backwards-compatible with the original LVM format.
The original LVM format is now discontinued and LVM2 should be considered mature and under active development. Most Linux distributions install LVM2 by default and may be invoked from the command-line via 'lvm'.
Excllent features but terrible to manage, a good graphical management software will greatly enhance its value.
[Edited by weLees, July 07]