The Response Code, Reason Code and other fields in the Chargent transaction have been returned to Salesforce by your payment gateway. If a transaction is declined or there is an error, you can often obtain more information by entering these codes into a search engine, or consulting the documentation provided by your payment gateway provider.
Here are some helpful links to understanding the decline reasons or support options for your specific gateway. Not all gateways have the response codes / reason codes listed on their website and may advise you to contact the issuing bank for the specific decline reason.