A half-draenei is theoretically the offspring of one draenei parent or half-draenei and another species. Apparently half-draenei of orc descent have few features that match that of the draenei. ([ )] Garona, and her son Med'an, show little draenei features like shiny eyes or chin spines on the latter, instead they look almost entirely orcish. Half-orc half-draenei is the full name to describe the race when one they are part half-orc and part half-draenei. Half-draenei is the short form. Orc-draenei half-breed is another way of describing this combination. Prior to Exodar crashing on Azeroth the only known half-draenei known ( would have had to been of )Lost Ones (and possibly Broken) descent).
They appear to be very rare, and far more rare than Half-ogres.
Garona is an orc-draenei half-breed, although she personally identifies with her half-orc heritage and others primarilly identify her as a half-orc. She and others believe her to be half-human (two speculative races were invented to describe her nature: near-humans and humans of Draenor descendant), this confusion was caused by Gul'dan who lied to Garona and told her she was half-human.
Brann Bronzebeard believes that she may "not" be a half-draenei as her features did not match that of the draenei or any other known race other than human, but it would seem unlikely that she was human due to her age, as she was already a young woman at the time of the First War. ( One explanation to this may be that Brann had never meet a half-draenei and doesn't know how they look like (although there is a section describing the half-draenei in )Horde Player's Guide it isn't told to be written by any in-universe character (). Other explanation may be that Brann had never met an )unmutated draenei and only knew the Lost Ones as Horde Player's Guide was written before the crash of the Exodar, so he may have compared her with the mutated draenei and he didn't find a relation.
Caydiem claimed that Garona's other half was "draenei" based on assumption that draenei were once human-like in appearance, before there was ever any knowledge that draenei were of the eredar race.
So far the term half-draenei has only been found in sources describing orcs. It might be possible that in settings describing other races the term might describe a half-draenei/half-other (in the same way as a draenei probably would use the term half-orc for a half-draenei/half-orc). It may also be possible that as was the case with half-human half-ogres, that a long description is given in order to designate any racial combinations that go outside the norm. In contrast, half-elf, half-blood elf, half-night elf, and half-orc are defined almost universally as races that originated from humans and the specified race. Half-draenei, half-ogre, and half-ogre mage are exceptions in that they so far only refer to races created through the interbreeding of orcs and a non-human race.