CSRSS stands for Client Server Runtime Server Subsystem.
It is a process created by Microsoft for the Microsoft Windows OS and it is usually found in the task manager as csrss.
exe.
It normally loads at boot time of the machine and its main function is of managing the majority of the graphical instruction sets under the Microsoft Windows Operating System platform.
The process csrss.
exe provides the functionality considered as a critical component of the operating system, and its termination whether intended or accidental can result to the display of the Blue Screen of Death.
Csrss.
exe is an essential subsystem that must be running at all times.
Csrss.
exe is responsible for console windows, creating and/or deleting threads, and some parts of the 16-bit virtual MS-DOS environment.
You will not be able to end this through task manager! It simply won't let you since it is used heavily by the system's kernel.
The csrss.
exe file is located in the C:WindowsSystem32 folder.
Any other location you find the csrss.
exe file, could spell out malware.
Csrss.
exe should not be present in versions of Microsoft Windows 98 and previous ones.
The Csrss.
exe process was started with the NT family of operating systems and continues to be issued with every version of Microsoft Windows till this day.
This is where the application splits itself into multiple simultaneous running tasks.
Threads supported by the process csrss.
exe are different from processes.
In fact one process can be split into many different threads all running concurrently taken a part of the process tasks and executing it at CPU level.
Processes and threads tend to vary from one another depending primarily on the underlying operating system of the host machine.
With the process csrss.
exe being the user mode portion, it is related to the kernel mode portion of the Win32 subsystem represented by the WIN32.
SYS process, which is required by the operating system to be constantly running in all instances.
Aside from being responsible for the threads and console windows, the csrss.
exe process is likewise accountable for some elements of the virtual environment of the MS DOS platform.
Basically, all instances of operations by the system that do not fall under the kernel mode are passed on to the csrss.
exe process.
Common Problems Encountered related to Csrss.
exe

1. Csrss.
   exe uses 100% of the CPU When you Right-Click an item in Windows Explorer or on the desktop
2. Your anti-virus is claiming that the file csrss.
   exe (which is needed and cannot be terminated in Task Manager) is the cause of a malware infection or problem.
   

Solution to these aforementioned frequently occurring problems

1. Before continuing, make sure you have backed up the contents of your My Documents folder, and any other important data stored in your profile such as application settings.
   Once your profile is deleted, you will not be able to recover data stored inside of it.
   In order to delete your profile, you must be logged in with an account which has administrative privileges which is also not yours.
   Once you are logged in, open the user profiles list.
   To locate the list of local user profiles, right-click My Computer, click Properties, and then on the Advanced tab, click Settings under User Profile.
   Select your profile from the list, and then click Delete.
   Logoff, and then log back on as yourself.
   A new profile will be created when you log on.
   
2. Locate the file Csrss.
   exe by going to Start -> Search and figure out if it is a Windows operating file by looking in the WindowsSystem32 and WindowsServicePackFilesi386 directories.
   The date stamps or last modified tag should be identical else if not, one of the csrss.
   exe files may be infected.
   Also check in your Startup folder.
   Csrss.
   exe should not appear there as it is supposed to be launched automatically during boot time by the kernel not by the startup folder.
   If it appears in the Startup folder, it should be removed.
   Delete the file once you have found it and decided if it is indeed a problem file.
   Csrss.
   exe can be a legitimate file and should not be removed just because you think it's harmful.
   Deleting the good one can cause the Blue Screen of Death.
   Use a little detective work to uncover the problem and clean up your computer junk files.
   CSRSS is definitely not a junk file so make caution when dealing with it.
   

Problems 1 & 2 are separate problems, as are their Solutions 1 & 2 are not related together.
The solution to problem 1 is solution 1, and the solution to problem 2 is solution 2.