What's the difference between professors?

Question

What is the difference between Professor, Associate Professor, Assistant Professor & Instructor?

I know it's something to do with tenure and expereince but more specifically...

Answer 1

The above answer is quite good, but I have a small quibble. Assistant professors do not have to apply for their jobs every two years. Assistant professors are tenure-track, and while they are evaluated every year, their jobs are secure .... unless they do not get tenure in their sixth year. Then they're screwed.

Answer 2

An instructor is someone teaching courses but is not on a tenure line. The person may or may not have their PhD.

An assistant professor - Generally has a PhD and is on a tenure track line. Most will be an assistant prof for 6 years at which time they will apply for rank and usually tenure. An Assistant prof has to apply for their job every couple of years. Rank and tenure are granted based on teaching, service and scholarship (research and publication). The mix and importance of these differ based on institution. Research 1 focus on publication and research 2 on equal of the three and research 3 more on teaching.

Associate professor - generally has taught in academia for 6+ years and has a record of teaching service and scholarship. May or may not have tenure with this (depends on the institution) some institutions will give a prof who comes in from another school rank but not tenure.

Full Professor - Has a significant publication, research, teaching, service record and is generally has a reputation in the field beyond a local level. Generally has been in academia for 10+ years.

Now people will use the term instructor and professor in generic ways as well.