A mentor is defined as someone that is able to advise or train. At work, a mentor could be a colleague from your department, or from another. Typically a mentor is senior to a mentee but this does not always need to be the case.
A mentor may share with their mentee information about his or her own career path, as well as provide guidance, motivation, soft skills development and role modelling. A mentor may also help with exploring careers, setting goals, developing contacts, and identifying resources that can support the mentee towards their chosen goal.
Typically, mentors are volunteers as it can be a great opportunity for self-development and an opportunity to give back.