In computing, a log file is a file that records either events that occur in an operating system or other software runs, or messages between different users of communication software. Logging is the act of keeping a log. In the simplest case, messages are written to a single log file.
A transaction log is a file (i.e., log) of the communications between a system and the users of that system, or a data collection method that automatically captures the type, content, or time of transactions made by a person from a terminal with that system. For Web searching, a transaction log is an electronic record of interactions that have occurred during a searching episode between a Web search engine and users searching for information on that Web search engine.
Many operating systems, software frameworks and programs include a logging system. A widely used logging standard is Syslog, defined in Internet Engineering Task Force (IETF) RFC 5424). The Syslog standard enables a dedicated, standardized subsystem to generate, filter, record, and analyze log messages. This relieves software developers of having to design and code their ad hoc logging systems.

View More On Wikipedia.org