Often a mentor is considered a ‘guru’, an expert with superior knowledge. Mentors share experience and give advice. A coach is not an expert. You are the expert in your life, in your career. A coach facilitates a learning and development process.
A coaching relationship generally has a set duration and agreed upon ways of working and is structured. A mentoring relationship on the other hand, is often a long relationship, that can be quite flexible and informal and often meetings take place when the mentee needs some guidance or advice.