SuperUser is an Application which will manage all the applications on the unlocked /rooted Android device . It helps in managing the applications having access to SU. With the help of this application any part of the rooted system can be modified with Super access. This application is made by two parts. Superuser.apk and the su binary
Superuser.apk shows you, a window with informations about denied or allowed apps and a log of the apps which used the su and when. The su binary: is what other apps access to get superuser rights.
Although All the ROMs comes preinstalled with SuperUser application.