Wikipedia
HRESULT
In the field of computer programming, the HRESULT is a data type used in Windows operating systems, and the earlier IBM/Microsoft OS/2 operating system, to represent error conditions, and warning conditions.
The original purpose of HRESULTs was to formally lay out ranges of error codes for both public and Microsoft internal use in order to prevent collisions between error codes in different subsystems of the OS/2 operating system.
HRESULTs are numerical error codes. Various bits within an HRESULT encode information about the nature of the error code, and where it came from.
HRESULT error codes are most commonly encountered in COM programming, where they form the basis for a standardized COM error handling convention.