The official definition goes as follows:
Organization Development (OD) is all the strategically planned interventions to increase an organization's effectiveness and health, using insights from the field of behavioral science.
This is what we make of it at Buildr:
We believe in the transforming power of organizations. We prioritize the needs of people and teams and the underlying beliefs and values they share before we start changing the type of work they do or the processes and tools they work with. Organizations where people's interactions are effective and meaningful are in for the long run.