What is OEI License

OEI doesn't exist in Microsoft products. The term you are likely referring to is OEM which stands for Original Equipment Manufacturer. Basically it's the full software license like retail licenses but can only be installed one one "computer" ever (retail is one computer at a time) and no phone/other tech support from microsoft
 

a_en

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DSP OEI ? I its Delivery Service Partner Original Equipment Install.
It is same as OEM, the license only work on the equipment you purchased alias non-transferable to other device.