Page rank and Traffic.

[canswift]

This may be obvious to "old-timers" out there, but I would like to understand Page Rank, as it relates (or not) to Traffic. Some domains I've seen for sale (like on TDNAM) will sometimes show monthly Traffic numbers (which is a good indicator of possible income if the domain is going to be parked). Other domain listings sometimes show Page Rank. Is Page Rank an indicator of Traffic, and possible domain income potential? My head is hurting on this one!
CanBrit