An executive coach is someone who specializes in developing an executive to optimize your leadership performance and more effectively manage increased overwhelm and stress.

There are many different levels of coaching:

The most basic type of coaching is when you need help overcoming a gap in your performance. This type of coaching is for people who are challenged with something that can either be apparent or it could be a blind spot that you may not be able to recognize. Either you or your boss assesses that your behavior impedes your performance or the performance of others and it should be addressed.
The next level of coaching is when you are promoted to management level. Here, you move from being an individual contributor to needing to understand the dynamics of developing others. In this stage, you experience a mind shift of letting go of control, trusting other people instead of being the hero, setting expectations, providing good feedback, and developing others.
Another level of coaching has to do with scale. When you go from managing five people to 100, or from 500 to 5,000, you must learn different ways to manage your time and lead your people.
Finally, executive coaching can range from trusted advisor to nuanced refinement for C-suite executives. Executives are already exceptional performers, but a coach will help you hone in on specific areas to optimize performance and unveil blind spots, bringing you data and feedback others may fear to offer.