Organization development, according to Richard Beckhard, is defined as:

(1) a planned effort
(2) organization-wide
(3) managed from the top
(4) to increase organization effectiveness and health
(5) through planned interventions in the organization's 'processes', using behavioural science knowledge"
(Smith, 1998, p261. Training and Development in Australia.)

According to Warren Bennis, organization development (OD) is a complex strategy intended to change the beliefs, attitudes, values, and structure of organizations so that they can better adapt to new technologies, markets, and challenges.

Warner Burke emphasizes that OD is not just "anything done to better an organization"; it is a particular kind of change process designed to bring about a particular kind of end result. OD involves organizational reflection, system improvement, planning, and self-analysis.

The term "Organization Development" is often used interchangeably with Organizational effectiveness, especially when used as the name of a department or a part of the Human Resources function within an organization.

Definition
At the core of OD is the concept of an organization, defined as two or more people working together toward one or more shared goals. Development in this context is the notion that an organization may become more effective over time at achieving its goals.

"OD is a long range effort to improve organisation's problem solving and renewal processess, particularly through more effective and collaborative management of organisation culture-with specific emphasis on the culture of formal work teams-with the assistance of a change agent or catalyst and the use of the theory and technology of applied behavioral science including action research"

[edit]
History
Kurt Lewin (1898 - 1947) is widely recognized as the founding father of OD, although he died before the concept became current in the mid-1950s. From Lewin came the ideas of group dynamics, and action research, which underpins the basic OD process, as well as providing its collaborative consultant/client ethos. Institutionally, Lewin founded the Research Center for Group Dynamics at MIT, which moved to Michigan after his death. RCGD colleagues were among those who founded the National Training Laboratory (NTL), from which the T-group and group based OD emerged. In the UK, working as close as was possible with Lewin and his colleagues the Tavistock Institute of Human Relations was important in developing systems theories. Important too was the joint TIHR journal Human Relations; although nowadays the Journal of Applied Behavioral Sciences is seen as the leading OD journal.

source : - Wikipedia