Mac OS X 10.6: Viewing system messages
While your computer performs tasks, it sends messages between applications, processes, and the operating system. Some of these messages are displayed, but most are not displayed because they can be too detailed and technical for most users. If you are a programmer debugging software, or are troubleshooting a problem with a service technician, information related to the problem may be found in these messages, which are stored in system logs. To view these messages, you can use the Console application, located in the Utilities folder in the Applications folder.
For more information, open Console and choose Help > Console Help.