Csrss.exe is one of the most important windows processes and the existence of this process could be vital. This process is used by the windows operating system to control a couple of tasks. The majority of the graphical instruction set of the Windows operating system relies upon this process. It may also be used to control the threading process in Windows(for those not familiar with threading, it is the technique which lets you split any particular application into the multiple instances).
Mostly there is a single csrss.exe process running in your system but if you find multiple instances of this process then don’t worry, as in many cases windows may run more than one instance of this process.
Also never try to terminate this process, as the consequences of terminating this process will be bitter, you will be taken to the blue screen of death.
In many mobile devices, this process controls some important power management features. Enjoy!