[this glossary is very preliminary and will be expanded in future]

Virtual inventory - this is my term for when a company does not actually own copies of all the titles it displays on its website. For instance, there might be 20,000 titles listed, but they only have stock for 7000 of them. The theory is that as customers add the items from the remaining 13,000 to their request lists, the company can order them in as required.

There is nothing inherently wrong with this approach, as many companies cannot initially afford to carry all of the titles they might possibly consider adding. The key is that the company should fully disclose the status of each movie, so that customers can determine which titles are not yet owned, as opposed to just currently rented out. Providing some indication of the policy on the ordering of virtual titles is also helpful - so that customers have a sense of what to expect in the way of future purchases of requested titles.

Weekly Package - a variant on the normal rental procedure whereby a company sends a single package of 2 or more discs to the customer each week. The customer must return the discs together as well. Usually the customer can have two packages out at any one time; the third is not sent until one of the first two is returned, and so on. Assuming the customer returns their packages on a regular basis, this provides a fairly predicable flow of discs (and costs).