Interchange is the rate charged to Credit Card processing companies, such as CDGcommerce, for using one of their cards. This is how Visa and Mastercard stay in business - they charge a percentage of the entire sale to the processor - which is eventually passed down to the merchant (you).
How the processor makes their money is they will add a certain percentage to the cost from visa and mastercard which they pocket. In this case, it is an extra 0.4% + $0.15 which is extremely cheap!! If you were to go to a company looking for a merchant account, you'd have to be a corporation doing many thousands of transactions monthly. But, because WeDJ.com has such a large member base, we were able to negotiate the incredible rate above on behalf of all our members.