A college professor is a person holding a formal academic position within an educational institution. The professor is in effect a senior lecturer, and is generally responsible for the oversight of education programs in his or her field. Being a professor is also a career achievement, and denotes a level of academic standing within the profession.
A college professor follows the normal academic training in whatever field or science, and typically progresses to postgraduate level employment in that field. With this employment comes a large range of work and studies which effectively raise their academic and professional level, providing advanced levels of experience and qualifications.
This form of career development provides multiple levels of qualification, training and experience, over and above the normal levels required for teaching. For example, a biology professor will have had experience in multiple areas of biology, including perhaps cell science, advanced laboratory techniques, database management, research system design, advanced research and other critical areas related to the academic professorial role.
Because professorships are rewarded by specific educational institutions, professorships are not 'transferable' in terms of holding academic office. However, the college professors progress by related forms of career development of holding offices in different educational institutions. A community college professor, for example, may progress to holding a professorial office in a major Ivy League college.
This type of career progression is not cosmetic. Career development in these roles is actually competitive tool to a large degree, because colleges employ the best applicants for these roles. Salaries differ considerably in these roles, and career advancement can actually be measured by the nature of the work , and roles involved in the professorship.
Professors are often prime movers in the advancement of education in their field. They are typically act as advisers to other educators, advisers to college boards, and as heads of departments within educational institutions. They're also usually heads of faculties, academic groups, and research management. This level of diversification of roles sometimes blurs the exact nature of career progression, that is generally slanted towards the individual's preferences and areas of specialization.