Some of my favorite descriptions of agile coaching from from Uncle Bob’s classic post “What Killed Waterfall could Kill Agile”:
XP defined the role of coach quite informally. The role would float between members of the team. One month it would be Joe, the next it would be Jane. It was not a title, and it conferred no authority. There were no decisions to be made, and no power of enforcement granted. The coach had the responsibility to remind, not to command.
The role of the coach was to act as a gentle reminder of process and discipline. The coach was never supposed to manage the project or the schedule! Indeed, these two roles were supposed to be adversarial! It is the project manager’s role to remind the team about the schedule and to encourage them to change something so that the schedule can be met. It is the coach’s role to remind the team to hold to the process. True XP coaches are not project managers nor are they team leaders. They do not lead the team to success, and cannot claim credit for that success. Indeed, the role is considered optional because mature teams will probably not need frequent reminders. But CSMs often assume the role of team leader. They are viewed as a critical component of the team; without whom the team cannot function. In XP a team without a coach is no big deal; but a scrum team without a scrum master is an oxymoron.
The International Coach Federation defines it well, too:
Coaching is partnering with clients in a thought-provoking and creative process that inspires them to maximize their personal and professional potential. Coaching honors the client as the expert in his/her life and work and believes that every client is creative, resourceful, and whole.
Standing on this foundation, the coach’s responsibility is to discover, clarify, and align with what the client wants to achieve; encourage client self-discover; elicit client generated solutions and strategies and hold the client responsible and accountable.