Stanley, oem means (original equipment manufacturer). It just letting the customer know this is made by the original manufacturer and not off brand. Hope this helps.

OEM DOES NOT MEAN IT IS MADE BY THE ORIGINAL MANUFACTURER, IF IT WAS, IT WOULDN'T SAY OEM. THIS IS NOT MADE BY RUGER, DESPITE WHAT THE OTHER ANSWERS SAY. An Original Equipment Manufacturer or OEM is a company that manufactures and sells products or parts of a product that their buyer, another company, sells to its own customers while putting the products under its own branding. This magazine is not made by Ruger, but made to Ruger standards and branded as Ruger. "This Ruger American .45 Auto/ACP pistol magazine is an OEM replacement magazine built to Ruger factory specifications and standards, ensuring proper fit and function in your Ruger American firearm. "

Stanley, Original Equipment Manufacturer which literally stands for (Factory). If a product is not OEM then it is made by a 2nd party and not the Original Equipment Manufacturer. Cheers and stay safe!

OEM stands for Original Equipment Manufacturer meaning that this is a Ruger-made magazine and not an off-brand magazine. I hope this helps!