fast - fast.exe
The process fast.exe is an integral part of the Microsoft PowerToys suite, used for switching users with a single mouseclick.
The file that corresponds to this process is normally found in the directory "%SystemRoot%\system32\fast.exe" (where %systemroot% is usually C:\WINDOWS by default).
The process fast is not in any way a virus, a worm, a Trojan horse, spyware, or adware.
It is a system process which can be terminated.