Turn - a Turn is the equivilant of our year.

Pass - a Pass is a period of time when the Red Star drops Thread on Pern which us roughly 50 turns(check the dragondex for more terms)

The time in Pern is long after the first people came to the planet in the Rukbat system. There is still thread falling from the skies.

For those of you who have read the Dragonriders of Pern series:

After Dragondawn and before The Skies of Pern. Before Aivas came.

Pern pretty much has no machinary and not much knowledge of any technology.