Imprint- Can be electronic (By swiping a card through a card reader) or manually (By obtaining a physical imprint using an imprinter). One of the two is always required to prove the card was present at the time of transaction (Retail).
ISDN Line- Line complying to industry standard digital network specifications.
ISO- (Independent Sales Organization) A Visa term for a company that is sponsored by an acquiring bank to solicit and sometimes support merchants.
Issuer- A bank that supplies credit cards to consumers.