OEM

Short for original equipment manufacturer, which is a misleading term for a company that has a special relationship with computer producers. OEMs are manufacturers who resell another company’s product under their own name and branding. While an OEM is similar to a VAR (value-added reseller), it refers specifically to the act of a company rebranding a product to its own name and offering its own warranty, support and licensing of the product. The term is really a misnomer because OEMs are not the original manufacturers; they are the customizers.
Contrast with IHV (Independent Hardware Vendor).
Buying OEM versions of Windows Vista: The Facts
Microsoft licenses OEM software to “system builders” which the license defines as “an original equipment manufacturer, or an assembler, reassembler, or installer of software on computer systems”. When asked, Microsoft says that OEM software is not intended to be installed by end users.
Is It Legal To Buy OEM Software?
In most cases like this, no. According to the Software & Information Industry Association Anti-Piracy FAQ, OEM software is illegal when not used in accordance with the software license.