Non-tenure-track positions: Individuals in these positions typically focus on teaching undergraduate courses, do not engage in research (except in the case of "research professors"), do not engage in departmental decision-making, and are not eligible for tenure.
Teaching assistant (TA) or teaching fellow (TF): Positions typically held by graduate students. TAs play a supportive role involving grading, review sessions, and labs. Teaching fellows (and at some universities, TAs) teach entire courses.
Adjunct instructor / adjunct professor / adjunct lecturer / faculty associate: Typically part-time non-salaried, non-tenure track faculty members who are paid for each class they teach. This position does not always require a completed PhD.
Instructor or lecturer: A full-time position at a university that does not involve tenure or a research program in the classical sense. This position does not necessarily require a PhD and usually involves teaching undergraduate introductory courses.
Collegiate Assistant Professor / Collegiate Associate Professor / Collegiate Professor: A recent advent, these instructors hold the full rank of tenured professors; however, they are not tenured. Often full-time instructors, their main purpose is to teach and conduct service to the students and university / college rather than conducting research or publishing.
Visiting assistant professor: A temporary assistant professor position (see below), e.g. to cover the teaching load of a faculty member on sabbatical.
Research professor: A position that usually carries only research duties with no obligation for teaching. Research professors typically must secure most or all of their salary from external funding sources such as grants and contracts. Although research professor positions usually are not eligible to be awarded tenure their ranks parallel those of tenure-track positions; i.e., research assistant professor, research associate professor, and research professor.
Tenured and tenure-track positions: These full-time faculty members engage in both undergraduate and graduate teaching, mentoring, research, and service. Only faculty in these positions are eligible for tenure.
Assistant professor: An introductory level professor. A position generally taken after receiving PhD and/or completing a post-doctoral fellowship. After 4–8 years, assistant professors will be either tenured or dismissed from the university.
Associate professor: A mid-level, usually tenured, professor.
Professor (sometimes referred to as "full professor"): a senior, tenured professor.
Distinguished professor / endowed chair (e.g., "the John Q. Smith Professor of Physics"): An honorary position in which a full professor's salary is increased by being tied to an endowment derived from the university, private individuals, firms, or foundations.
Professor emeritus/emerita: An honorary title bestowed on retired faculty members who have attained the rank of professor.