So what do you understand by the term 'OEM'? e.g. 'OEM' battery, lens cap etc. Asking this question as I have seen quite a number of threads in buy/sell that use this term. What I understand by Original Equipment Manufacturer is that the Canon/Nikon/etc branded parts that was manufactured by someone else. "Third party" would refer to branding other than the Canon/Nikon/etc themselves.
What's your understanding?