If you redirect HTTP requests to other pages within the same website, each of the original HTTP requests will be followed by a redirection HTTP request, which will contain the same referrer and, consequently, the same referrer search string. Webalizer will count each request individually, reporting two hits for this referrer and the search string contained in the referrer.
To circumvent this, referrers and referrer search strings will be ignored for redirected URL paths listed in the 'Ignore Redirected HTTP Requests' field.
More information about ignoring redirected HTTP requests can be found here.
Please note: Only the Stone Steps version of the Webalizer is able to interpret this parameter.