The following is the answer:

Csrss.exe - You cannot end this process from Task Manager.

 - This is the user-mode portion of the Win32 subsystem (with Win32.sys
being
  the kernel-mode portion). Csrss stands for client/server run-time
subsystem
  and is an essential subsystem that must be running at all times. Csrss is
  responsible for console windows, creating and/or deleting threads, and
some
  parts of the 16-bit virtual MS-DOS environment.