What CyanogenMod is
CyanogenMod (/sɪˈænoʊdʒəŋmäd/) is a customized, aftermarket firmware distribution for select Android devices.
Intended as a replacement for the software (also known as the "firmware" or "ROM") that comes factory installed on your smartphone, CyanogenMod is based on the Android Open Source Project – the same base software used in all Android phones. However, CyanogenMod offers several benefits over the pre-installed firmware, including vastly flexible interface andcustomization, a wider set of new features, and sometimes significant improvements in performance.
CyanogenMod's features may allow you to bypass software limitations imposed by carriers, which may prevent you from using the handset in a manner that they do not support. Such features include, but not limited to, the ability to overclock the phone's CPU, tether your phone to your computer, or fully back up your phone to your SD Card.