The linux kernel device mapper is the lvm (linux logical volume management) team's implementation of a minimalistic kernel-space driver that handles volume management, while keeping knowledge of the underlying device layout in user-space. this makes it useful for not only lvm, but software raid, and other drivers that create "virtual" block devices.

this package contains the (user-space) header files for accessing the device-mapper; it allow usage of the device-mapper through a clean, consistent interface (as opposed to through kernel ioctls).