A value-added reseller, or VAR, is basically any B2B (business-to-business) vendor which specializes in a particular field of hardware and/or software, along with any related installation, service, and upgrades. Smaller companies can distribute their products through these resellers. A VAR will often advertise in the appropriate trade magazines, which give out free subscriptions to anyone who can fill out a card and convince the publishers that they make corporate purchasing decisions. VARs come in all sizes, from Mom-and-Pop family businesses to gigantic mega-corporations.
As an example, a data warehousing VAR might sell high-capacity storage systems in multiple formats, OCR/document scanning equipment, as well as the applications to label, index and retrieve the information. Their customers might include both a huge pharmaceutical company, and a small-town credit union with a budget a fraction of the size of the drug maker's.
The VAR helps the customer to determine the best solution for their level of need by bringing many different products and product lines together for comparison. There is some agreement that the more specialized a VAR is, the better its service. As a consumer analogy, would you rather buy a new camera at Wal-Mart, or at your local camera shop? This is where the "value-added" part comes in: expertise in a particular subject area.
Well, that's about it for this introduction to VARs...in the course of my work day I am exposed to a lot of this marketing terminology and have had to figure it out largely on my own. Hopefully this will help you out if you ever have to deal with this side of the high-tech industry.