Management is the process of coordinating and integrating work activities so that they are completed efficiently and effectively with and through other people.

Here, efficiency is defined as the relationship between inputs and outputs, the goal of which is to minimise resource costs. Effectiveness is the attainment of goals.

Most management textbooks give four functions of management:
  1. Planning: Includes defining goals, establishing strategy, and developing plans to coordinate activities.

  2. Organising: Determining what tasks are to be done, who is to do them, how the tasks are to be grouped, who reports to whom, and where decisions are to be made.

  3. Leading: Includes motivating subordinates, directing others, selecting the most effective communication channels, and resolving conflicts.

  4. Controlling: Monitoring activities to ensure that they are being accomplished as planned and correcting any significant deviations.
Management can therefore be viewed as a process: it is the set of ongoing decisions and actions in which managers engage as they plan, organise, lead and control.

Sources:
Hales, C.P. "What do managers do? A critical review of the evidence', Journal of Management, January 1986, pp. 88-115.
Koontz, H and O'Donnel, C. (1955) Principles of Management: An Analysis of Managerial Functions. McGraw-Hill, New York.
Robbins, et al. (2000) Management. Prentice Hall, Australia.