Extended Log Format (ELF) is a standardised text file format, like Common Log Format (CLF), that is used by web servers when generating log files, but ELF files provide more information and flexibility.
Example
#Version: 1.0#Date: 12-Jan-1996 00:00:00#Fields: time cs-method cs-uri00:34:23 GET /foo/bar.html12:21:16 GET /foo/bar.html12:45:52 GET /foo/bar.html12:57:34 GET /foo/bar.htmlReferences
Extended Log Format Wikipedia(Text) CC BY-SA