The term mentor has been used for some time to describe someone that supports a more junior person in their career.
The term sponsor is a more recent title for someone who seemingly does something similar, but, in fact, there is quite a difference in what they bring to an individual and what they expect in return.
A mentor is an adviser. They are someone that can provide perspective on your role, career and situation. They can help you work out what you are really good at or what you need to be good at to shine in the organisation.
They understand the organisation and its politics and can help you to navigate the corporate ladder. They can help you define your strengths, weakness, challenges and potential career journey and they can put you in contact with influential people. That influential person could be a sponsor.
A sponsor is the person that could make your potential career journey a reality. If someone decides to sponsor you it is because they believe in you. They will do all they can to help you succeed because, once they have chosen you, you, in effect, carry their brand.
They can make you visible to the top people inside and outside of your organisation, they can help with pay rises and promotions and get you involved in high-profile assignments. They will also offer protection in times of trouble.
Mentors are often people with whom you share an affinity, who can empathise with you and your situation; sponsors offer serious seniority, power and influence.
Mentors will expect little in return for their advice and support; sponsors will expect you to deliver for them and make them look good. To a mentor you are their mentee; to a sponsor you are their protégé.
Seek out both. They will make all the difference to your career.