PHP Notice: Use of undefined constant rootMP3URL - assumed rootMP3URL

I keep getting this error message PHP Notice: Use of undefined constant rootMP3URL - assumed rootMP3URL

 // Remove the PHP script name from the URL.
        if ($stripScriptName) {
                //$rootMP3URL =  substr($rootMP3URL, 0, strrpos ($rootMP3URL, "/")); // Trim off script name itself
                $webFolder = dirname($webFolder);
                $options['$rootMP3URL'] = dirname('rootMP3URL');

                $debugger->debug("dirname({$options['$rootMP3URL']}) = " . dirname('rootMP3URL'));
                $debugger->debug("dirname($webFolder) = " . dirname($webFolder));
    }