Consult or not to consult? That is the question.

What do consultants do? And what does one have to do in order to be a consultant? I don't recall seeing that as a major during my undergrad years. It was a regular assignment each semester in business school. But what does it really mean to be a consultant? Do I need to be an expert, mentor, coach, sounding board or all of the above? Who in their right mind is going to pay me for my 'considered opinion?' Consulting, it' not for sissies!