A professional service is a service requiring specialized knowledge and skill, usually of a mental or intellectual nature. It is a service that is delivered to the customer by using a significant human intervention/involvement.
Examples of professional service:
Consultancy (including consulting through email)
Brand architecture (incl. creating logos, slogans etc.)
Content development and strategy
Photography or any other individually commissioned content sent in a digital form
Software development and design
Educational or professional courses where the content is delivered by a person during a live session via the internet or an electronic network (vs pre-recorded content)