The essence of coaching
I recommend a concise and comprehensive definition of coaching, adopted from the major international association of coaches - the International Coach Federation (ICF)
Coaching is partnering with clients in a thought-provoking and creative process that inspires them to maximize their personal and professional potential
Such a definition of coaching includes all the elements essential to understanding the essence of coaching and to distinguish it from other forms of cooperation.
Partnership is a collaboration of two (sometimes more) equal persons who engage in joint implementation of the agreed goal. This cooperation is based on the definition of two roles - the client and the coach. The aim of this cooperation is to maximize the personal and professional potential of one (or more) people, whom we call clients. The coach is the person who helps to achieve this objective, based on their skills and experience. The coach moderates the process in a creative and inspiring way.
Accepting such a definition makes it possible to distinguish coaching from consulting, counseling, mentoring and teaching.
More reading on this topic (in the form of questions and answers) is available on the ICF page Coaching FAQs and in the Polish translation here.