A clear definition is buried in an early 1980s Watchtower article. The idea is that, since the Bible was written under the active direction of holy spirit, and Watchtower leaders follow the Bible, it can be said that, in effect, these leaders act under the direction of holy spirit.
This idea obviously has many problems.
In the mid-1970s there arose a really stupid situation in the congregation I was attending, and the elders acted like the Keystone Kops in getting the problem resolved. It was clear to me that they were not acting under the direction of holy spirit, so I questioned several elders about why the Society made a claim that elders are appointed by and act under the direction of holy spirit, when it was obviously not true. Eventually the CO sat down with me and explained what the Society really meant. At the end of our conversation I said, "Let me get this straight: elders are not directly appointed by holy spirit?" He literally hung his head and looked at the floor, and said "Yes." Well, I was pretty pissed at that point, because I realized that the Society was deceiving the JW community by never clearly explaining this doctrine, but was always repeating "you must obey elders because they're appointed by holy spirit!"
In the mid-1980s I argued with my stepdad, who was an elder, about this. He understood the Society to be saying that elders are indeed directly appointed by holy spirit and that bodies of elders make decisions via direct intervention of holy spirit. He refused to believe what the CO told me, and refused to understand what the Watchtower article said. So it's obvious that the Society's lies are believed by most JWs.
The claim that JW leaders and elders are in effect directed by holy spirit is pure doubletalk. It assumes that these men perfectly follow the Bible's direction -- which is demonstrably false. Anyone at all can make the same claim. But JWs reject that claim by all but themselves. Two standards are at work here.
AlanF