There is a vast literature about coaching with dozens of definitions and comparisons with similar or contiguous methodologies. The word has not been translated and it is also used with many different meanings.
Here is a selection of three complementary definitions, with the explanation of the reasons why they were chosen.

The first definition is from ICF – International Coach Federation – the largest professional coaching association in the world, which through its 21.400 associates in over 110 countries takes care of the progress of the art, the science and of the practice of Professional Coaching.
ICF defines coaching as partnering with clients in a thought-provoking and creative process that inspires them to maximize their personal and professional potential.
This definition, chosen because of the authority of the source, is part of a set of rules that ICF proposes to its members and to coaches who require certification. For more details, in particular about the ethical code, see www.icf-italia.orgwww.coachfederation.org

The second definition is due to Timothy Gallwey, mentioned by Sir John Whitmore: Coaching is..to unlock a person’s potential to maximise the performances… not by teaching, but by helping to learn.
This definition, generated by the person who first used Coaching in sports, makes it clear that this methodology has as its primary purpose the improvement of the performance and that the Coach is not a teacher or an expert but someone who accompanies learning by creating an enabling environment.

The third definition explains in clear and simple terms how a session actually takes place: the process of coaching is fundamentally a conversation, a dialogue between coach and client in a productive and result-oriented context. A conversation in which, by asking the right questions at the right time, the coach encourages and helps to consider different perspectives and strategies, where “a productive and result-oriented context” is referred to the client’s positive and proactive attitude, which makes him/her responsible for achieving the result.