Join Date: Nov 2009
Location: District of Columbia
Device(s): LG G2, Moto G, Galaxy S3, Galaxy Nexus LTE, Nexus 7, HTC Flyer
Thanked 6,107 Times in 4,005 Posts
Clockworkmod is a custom recovery for rooted devices. It replaces the stock recovery when flashed. It's used for backing up your device (nandroid) and flashing ROMs, kernels, themes, apps etc. This among quite a few other features. If you're looking to root your device, it's highly advisable to flash a custom recovery (doesn't have to be CWM, can be TWRP or others).