Interac Online is where you use your bank card to fund your account much like using a credit card to make a purchase online. It's only compatible with TD, Scotia and participating credit union bank cards without a Visa or MasterCard logo on them. Interac e-Transfer is where you login to your online and execute an Interac e-Transfer payment that is pushed to via email by the Interac network.
List of financial institutions that support Intearc Online: http://interac.ca/en/interac-online-consumer.html
About co-bdaged (Visa/MasterCard) debit cards: http://interac.ca/en/co-badged-cards.html