Is there such a thing as "internal" vs "external" rotor venting?

If someone says there is such a thing as internally vs externally vented brake rotors (for cars) - what could they mean?
If you have a rotor formed by 2 plates, the plates separated by an air
gap formed by a structural web or matrix or separators, then what additional aspect of their construction would lead to one being called an internally-vented rotor while a second would be called externally vented?
(supposedly for the LH-era 300m there was a difference between the PHP vs non-PHP option package in terms of the front rotors being internally vs externally vented, something that may or may not have any findable authoritative source...)
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