A "trusted role model, adviser, wise person, friend, Mensch, steward, or guide - a person who works with emerging human and organizational forces to tap new energy and purpose, to shape new visions and plans, and to generate desired results. A coach is someone trained and devoted to guiding others into increased competence, commitment, and confidence."
F. Hudson, 1999

"What makes a good coach?"

"A good coach is someone qualified, objective, and skilled at motivating behavioral change. It's a person who can establish rapport with a wide range of people, ask the right questions, assess problem behaviors, and keep track of effective and not-so-effective behaviors. It's important that the individual suspend judgment and be a helpful colleague, not a competitor."
"Another important coaching skill is an understanding of how to criticize constructively, be sensitive when pointing out problems, provide positive encouragement, and care for the self-esteem of the 'coachee.' Then end result of good coaching is improved business performance for the individual and saving a valuable resource for the company."
D. A. Benton, Secrets of a CEO Coach.

"Business coaching is an intentional relationship between two or more people that facilitates shifts in the thinking, behavior and performance of the business person. Business coaching enables the business person to be in a position to grow and achieve goals that they consider important. Business coaching is an interactive process that expands business peoples' effectiveness at both business and life-skills and allows them to identify obstacles that can hinder them from moving forward and attaining their goals."
Quantum Leap Success Coach- Executive, Career, & Business Coaching.