syslog is a standard (RFC 5424) for message logging. Use this tag for syslog logging related messages. For generic logging messages use [logging] instead

Standardized by the RFC 5424, it is a de facto standard to manage system logs on network assets and Unix-like operating systems. It is a client/server protocol used to centralize log messages, but many times configured to deliver local only logs.

It have facility codes that define what type of sofware created a log entry and severity levels to better separate messages to be interpreted by a sysadmin, or integrate with a monitoring tool.

Further Reading: