'A consultant is usually an expert or a professional in a specific field and has a wide knowledge of the subject matter. A consultant usually works for a consultancy firm or is self-employed, and engages with multiple and changing clients. Thus, clients have access to deeper levels of expertise than would be feasible for them to retain in-house, and to purchase only as much service from the outside consultant as desired. It is generally accepted good corporate governance to hire consultants as a check to the Principal-Agent problem.' 'Consultant' is also the term used to denote the most senior medical position in the United Kingdom, Australia and Ireland (e.g., a consultant surgeon).Bold text
More recently the term is also used euphemistically for temporary staff. That resource is only temporarily employed by a company to augment the company's core set of employees without providing any unique expertise. This usually indicates that the consultant could be expended when demand for that particular skill diminishes, though this expendability is sometimes recompensed with higher pay. In this usage, the consultant is usually employed through a limited company which they themselves own, or through an umbrella company. Consulting has come under some criticism because of staff augmentation and the high amount of jargon consultants use, also known as consultantese.
Sometimes a consultant is not an independent agent but is a partner or an employee of a consultancy, that is a company that provides consultants to clients on a larger scale or in multiple, though usually related, skill areas. This has advantages both to the client and to the consultant by:
Strategy consultants are common in upper management in many industries. There are also independent consultants who act as interim executives with decision-making power under corporate policies or statutes. They may sit on specially constituted boards or committees.