What is the difference between counselling and psychotherapy?

In the context of mental health, "counselling" is generally used to denote a relatively brief treatment that is focused primarily on behaviour. It often targets a particular symptom or problematic situation and offers suggestions and advice for dealing with it. It is usually short term.
Psychotherapy is generally a longer-term treatment that focuses more on gaining insight into chronic physical and emotional problems. Its focus is on the person's thought processes, and how these may be influenced by past events such that they cause problems in the present. In other words, psychotherapy addresses the root cause and core issues of current problems so that lasting change and personal growth may occur.
There are several different types of therapy that fall under the general heading of psychotherapy, including approaches such as cognitive behavioural therapy, dialectical behaviour therapy, psychoanalytic psychotherapy, and much more. I am a qualified integrative psychotherapist and counsellor.