ID — A permanent, unique identification code given to a record in a database.

Inactive buyers — The portion of a list which has not shown any purchasing activity for a set period of time.

Income — A demographic selection factor on consumer lists, selectable in $1,000 increments.

Individual — A mailing that goes to one specific recipient, as opposed to "occupant" mailing.

Inquiry — A request for a sample, catalog or more information.

Installment buyers — Purchasers who split the total price of a product up and divide it evenly over periodic payments, usually monthly.

Insurance lists — Consumer lists compiled by insurance companies based on the type and amount of insurance owned.

Interactive marketing — Sales that take place via computer, with the buyer learning about and making purchasing decisions about products online.

Interlist duplicate — An address record that appears on more than one list.

Intra-file duplicates — An address record that appears more than once on the same list.

Invalid records — Records with errors that make them unusable, and which often must be removed from a list and manually fixed.