Coaching and (Psycho)Therapy are both individual processes that use psychological methods and interventions to support people who are seeking help. The coachee and her or his thinking, acting and feeling is the focus of the process. One of the most crucial criteria if a process for either of them is successful depends on a working relationship between coach/therapist and client/patient.
But there are clear differences: coaching is always willingly and for people who are able to self-manage their daily routines and are clinically “healthy”. If it’s not the case a (psycho)therapy is the right way to (re)establish psychological health. Furthermore coaching focuses on personal and professional growth in the present and actionable strategies for a dedicated goal in the future whereas therapy often focuses on the past and difficulties arising from the past causing emotional dysfunction.  

More info can be found on the International Coach Federation FAQ page