The logger facilitates logging messages to an adapter. A typical logging adapter would be a file or syslog, of course this can be expanded to support other logging systems very easily.
Log levels are used to determine the severity of a log entry
The available log levels are debug, info, notice, warning, error and critical. These are the most common and widely used log levels.
Of these log levels, notice, warning and error are also used by the error handler to log PHP errors. These levels very closely correlate with PHP error levels.