| Word | Description |
| INRIA | Institut national de recherche en informatique et en automatique (INRIA) (English: National Institute for Research in Computer Science and Control) is a French national research institution focusing on computer science, control theory and applied mathematics. |
| Installation Root | The file system directory where the shopping cart is installed, e.g. /var/www/html/zencart or /var/www/html/oscommerce |
| Interac Online | The Interac Online, or IOP, service is a new payment option that allows you to pay for goods and services on the Internet directly from your bank account. This service is only available in Canada. |
| Interchange | The exchange of transaction data between the merchant bank and customer card issuing bank. |
| Invalid Transaction Tag | Response usually displayed when the tag sent does not match the transaction previously sent - for example, Tag A was returned from E-xact with Purchase #1 but Tag B was sent by the merchant with Tagged Refund #1. This can also occur if the transaction that is being refunded or completed is too old (customers have up to one year to refund charges and around 5 days to complete pre-authorization type transactions). |
| IP | Internet Protocol. The Internet protocol defines how information gets passed between systems across the Internet. |
| ISP | Internet Service Provider. A company that provides individuals and businesses with access to the Internet. Many ISPs also provide website hosting services. |
| IVR Telephony | Integrated Voice Response Telephony technology creates automatic message selections through phone systems. E-xact's software can be used in IVR telephony. |