Another way to put it is trunk(ing) of a tree. The trunk between roots and branches allows the smooth flow of nutrients in a small bundle of fibers, a trunk or "bundle" of radio frequencies do the same thing. Rather than waiting through transmissions and dead air on an individual frequency the radio scans quickly through the bundle and uses the first dead air it comes to. Each transmission is "tagged" on the data channel so the other radios in the system can follow and not lose each other. Nature abhors a vacuum and so does a trunking system so by filling it with transmissions dead air is minimized making the most efficient use of air time and frequency spectrum, each "talk group" doesn't require it's own frequency.
And there you have it for the non-wiki subscribers.
"While it is true, that there are no dumb questions, only dumb answers (as often shown here)."
How true.
"(I'm joking!)"
I'm not, some are quite entertaining. Keep 'em coming, Hamsexy NEEDS you!