An organisation with a simple structure does not have an elaborate, formal arrangement of reporting relationships. Work relationships are more fluid. There is a small, centrist management hierarchy. There are few functional specialists.
People doing core operational tasks are often interchangeable.
The division of labour is looser with people carrying out multiple roles. There is less role differentiation. Thus it is the CEO that shapes strategy. It will generally reflect what they want, believe in, their interpretation of the world and there commitments. She knows her company and the business environment through and through.