Merchant Account
A merchant account is a contract under which an acquiring bank extends a line of credit to a merchant, who wishes to accept payment card transactions of a particular card association brand. Without such a contract, one cannot accept payments by any of the major credit card brands.
All-in-One package
Merchants will need both a Merchant Account and a Payment Gateway in order to accept payments. Some Entities offer both a Merchant Account and a Payment Gateway. QuickBooks Merchant Service (QBMS) is one example. As an added bonus, QBMS also provides a mechanism to import your sales (orders) directly into your QuickBooks software accounting package. Combining QuickBooks Merchant Services along with UltraCart constitutes a great "all-in-one" package.
If you don't already have a merchant account it's best to do a little research to determine what client will best fit your needs.