"Pro Tem" is the term used at the University of Oregon to describe faculty who are often called "adjunct faculty" on other campuses. Here, Pro Tem means "temporary" in that Pro Tem positions are intended to last a maximum of three years. The Pro Tem designation does not describe the FTE of a position nor indicate that the position is less than half-time; it only designates the temporary nature of the position.
In certain rare cases, departments or units can petition the Provost asking to extend a Pro Tem position beyond the three year limit. When such a petition is granted, a faculty member filling that position CANNOT stay in the position.
Faculty who are hired into a Pro Tem position should expect to be working for the University of Oregon for a maximum of three years. Continuing at the University of Oregon can only happen if a Pro Tem position is reclassified to a Career NTTF position - and then the faculty member holding the position will often need to reapply for the position - or if the faculty member is hired into a different position.
On rare occasions, a faculty member can petition the Provost to have their position reclassified as Career. You can read more about how to do that here.