syslog is a standard for logging messages about the operation of a system.
syslog is a standard that defines the format of messages about a system's operation. They are further categorized by facility (user,mail,kern), etc and a severity (critical, emergency, informational, etc). These messages are usually then processed by a network monitoring system to take appropriate action. For example, on an emergency message, staff could be paged to resolve the issue, whereas long term analysis could be done on informational messages to properly maintain sytems.