Mac OS X keeps many records or logs of "things" that happen on the system.  For example the printing system uses the Common UNIX Printing System or CUPS.  The CUPS system writes a sentence or more of text to one of three files in the folder /var/log/cups: access_log, error_log, and page_log.  So if there was an issue printing a document we might want to use /Applications/Utilities/Console.app to view the error_log file for CUPS.  There are many other useful logs but especially so are system.log, console.log, panic.log, and any logs in ~/Library/Logs/CrashReporter or /Library/Logs/CrashReporter.  Almost all the logs in the system are conveniently accessed using the Console application.