1. The UNIX/Linux System Logger, where all system messages or errors are stored. From I-gloss

2. On UNIX, syslog is the standard logging facility. Programs call the syslog() function, and their messages end up somewhere in the /var/log directory. The syslog facility can also be configured to forward alerts from one UNIX machine to another (using un-authenticated UDP datagrams to port 514). Key point: When analyzing a machine that was broken into, you may find interesting information in the syslog logs. In particular, buffer-overflow attempts have distinctive messages, such as messages claiming an unknown command where the command is a string of binary characters. From Hacking-Lexicon

3. The UNIX System Logger. From Linux Guide @FirstLinux