A zacron was a unit of length. The Earth equivalent is unknown.
Staanz warned the crew of a nearby flax, which was a "magna-drift mesh 75 million zacrons long." ("The Flax")
The unit was also mentioned in the Farscape RPG, referring to the planet Tianna, which was said to be one of the few resort worlds within the Uncharted Territories and the only one within 500 million zacrons of space.