In the broad sense intended here, a mentor is someone who takes a special
interest in helping another person develop into a successful professional.
Some students, particularly those working in large laboratories and
institutions, find it difficult to develop a close relationship with
their faculty adviser or laboratory director. They might have to find
their mentor elsewhere—perhaps a fellow student, another faculty
member, a wise friend, or another person with experience who offers
continuing guidance and support.
In the realm of science and engineering, we might say that a good mentor
seeks to help a student optimize an educational experience, to assist
the student’s socialization into a disciplinary culture, and to
help the student find suitable employment. These obligations can extend
well beyond formal schooling and continue into or through the student’s
career. (Link)