Coaching is a process to support and enable people work towards goals that they have identified. Unlike mentoring, it does not require expert knowledge about the coachee’s work area and is mostly forward looking rather than addressing and dealing with events that have already happened (for example counselling).
I will be clear with clients if I consider that their goal/challenge is something that another specialism would be better suited to address. (I am also a mentor, but I use a number of different skills in either mentoring or coaching sessions.)