LVM is a Logical Volume Manager for Linux. It offers a management of the disk space which is more flexible and less limited than the standard disk partitioning based on primary and logical partitions. LVM is supported by all the major Linux distributions, and it's even used by default on Fedora and RHEL.
This documentation has been written for multiple reasons: it will quickly tell you the basics if you have never heard of it before in the first chapter. It also gives you an idea of whether or not LVM is good for you. The second chapter explains more about how LVM actually works so that you know what it can do and how to fix problems related to LVM. The next chapters explain how the Linux boot process works when LVM is used for the root filesystem. The fifth chapter explains how to make reliable backups using LVM snapshots.