Most browsers ship with built-in developer tools. These developer tools usually include a console. The console gives you information about the page that's currently running.
Messages logged in the console come from
either the web developers who built the page
or the browser itself.
All console messages have a severity level:
Verbose, Info, Warning, or Error.
An Error message means there's a problem on your page that you need to resolve.
How the Lighthouse browser error audit fails
Lighthouse flags all browser errors logged to the console: