The ErrorLog directive in a web servers configuration file (e.g. httpd.conf) is used to define the location of various log files, such as the error log, something like this.
With this configuration, the error log would be located at:
As the name implies, the error_log will capture events classified as an error. Here is an example of an error in error_log.
[Fri Mar 20 21:21:28.084472 2020] [unique_id:alert] [pid 3538:tid 139812487051072] (EAI 2)Name or service not known: AH01564: unable to find IPv4 address of "server1" AH00016: Configuration Failed
When using the apachectl command to start or restart the web server, the -e option followed by a log level (such as debug) can be used to append additional details to the error log.