A log file is a recording of everything that goes in and out of a particular server. It is a concept much like the black box of an airplane that records everything going on with the plane in the event of a problem. The information is frequently recorded chronologically, and is located in the root directory, or occasionally in a secondary folder, depending on how it is set up with the server. The only person who has regular access to the log files of a server is the server administrator, and a log file is generally password protected, so that the server administrator has a record of everyone and everything that wants to look at the log files for a specific server.
Servers are not the only system that use log files. Process control systems, as well as computer operating systems have logging subsystems that work exactly like a log file does. While these are more sophisticated than a simple log file, most times it is the same concept, where a log message is recorded in the file and saved until it is needed. Other forms of log filing use more sophisticated systems, some of which even analyze the logs before they are needed, but it all depends on where the log file is located.
The point of a log file is to keep track of what is happening with the server. If something should malfunction within a complex system, there may be no other way of identifying the problem. Log files are also used to keep track of complex systems, so that when a problem does occur, it is easy to pinpoint and fix. Log files are also important to keeping track of applications that have little to no human interaction, such as server applications. There are times when log files are too difficult to read or make sense of, and it is then that log file analysis is necessary. Log file analysis is generally performed by some kind of computer program that makes the log file information more concise and readable format. Log files can also be used to correlate data between servers, and find common problems between different systems that might need one major solution to repair them all.