Link2SD is an application manager that makes it easy for Android 2.0+ users on their device to move applications to the SD card. It enables you to manage your apps and storage easily.
Link2SD uses a secondary partition on your SD card and uses it as another segment of internal storage.
Link2SD moves apk, dalvik-cache (.dex), lib and internal data files into this partition, which the OS mounts on boot, and creates a symbolic link in the original location.
This retains the file structure that the system expects but with the bulk of the data moved to the SD card.