Here’s the answer given by the International Coaching Federation:
Professional coaching focuses on setting goals, creating outcomes and managing personal change. Therapy deals with healing pain, dysfunction and conflict within an individual or in relationships. The focus is often on resolving difficulties arising from the past that hamper an individual’s emotional functioning in the present, improving overall psychological functioning, and dealing with the present in more emotionally healthy ways. Coaching, on the other hand, supports personal and professional growth based on self-initiated change in pursuit of specific actionable outcomes. These outcomes are linked to personal or professional success. Coaching is future focused. While positive feelings/emotions may be a natural outcome of coaching, the primary focus is on creating actionable strategies for achieving specific goals in one’s work or personal life. The emphases in a coaching relationship are on action, accountability, and follow through.
I would add that coaching tends to be of a much shorter duration than therapy. In my work, if I were to meet with a client twice per month, a client of mine could expect our coaching work to last between 5 and 8 months. Therapy would traditionally be much longer.