What does CTO mean?
It is quite difficult to clearly define what a technical director is doing: the profession is in demand in a wide variety of areas (manufacturing, construction, IT, television, etc.). The duties of a specialist in any of the above areas include coordinating the technical development of the enterprise, monitoring the effectiveness of design solutions, advising the team and managing the work of personnel.
Now every startup has a similar team. You can read more about CTO roles and responsibilities here.