OE and OEM products are products from manufacturers who make the original factory Genuine part for the car as well. For example, BMW doesn't manufacture and produce a control arm - Lemforder makes it for BMW and engraves the BMW logo during production. Buying directly from Lemforder instead of the BMW dealership means that you get the same quality part for a lot less cost. We typically recommend the OE/OEM alternative.
Complete details with comparison pictures are here: https://www.fcpeuro.com/page/oe-academy
