csrss.exe is a legitimate Windows system process, part of the Client/Server Runtime Subsystem. On a healthy system it normally runs from the Windows system directory and helps the operating system manage essential session-level functions. Because it is a well-known name, attackers often imitate it with a fake binary or a similarly named file to look trustworthy during quick reviews.
This matters in cyber security because process-name trust is easy to abuse. A malicious csrss.exe may be used for persistence, defense evasion, or to blend into normal admin noise while other payloads run. Defenders should verify the file path, digital signature, parent process, and launch context, and treat any unexpected csrss.exe instance outside the standard Windows location as suspicious until proven otherwise.