From the Oxford English Dictionary:

Mentor – “An experienced and trusted adviser.”
Mentoring – to “Advise or train someone.”
Consultant – “A person who provides expert advice professionally,” i.e., for remuneration.
Consulting – “Engaged in the business of giving expert advice to people working in a professional or technical field.”

There are many definitions of mentoring and consulting (and coaching, training, …) to suit the needs of those so engaged.
For our purposes:

  • Mentoring is an informal and unpaid relationship where the majority of the work is done by the customer (mentee).
  • Consulting is a formal, personalised, and paid relationship where a significant amount of tangible or intangible value is provided by the consultant.
  • We move between mentoring and consulting relationships following communication and mutual consent.