OEM (Original Equipment Manufacturer) toner refers to any new toner cartridge that was manufactured by the company which also built your copier or printer. So, if you own an HP printer, only HP manufactured toner can be considered OEM.
OEM toner cartridges are typically considered to be of high quality, with low failure rates and can be counted on to be compatible with your device. However, manufacturers charge a premium for their toner, and it is typically much more expensive than new compatible or remanufactured toner cartridges.
Our article The Difference Between OEM and New Compatible Toner Cartridges compares when you should consider OEM toner and when can save a few dollars with new compatible toner.