For years I have worked as a contact consultant. That means that organizations (mostly Corporations) hire my boutique firm The Business Channels for Business Productivity Training, Process Improvement and/or Project Management.
Today the term "consultant" is used in a lot of different ways but this is how I have always worked.
A consultant (from Latin: consultare "to discuss") is a professional who provides professional or expert advice in a particular area such as security (electronic or physical), management, accountancy, law (tax law, in particular), human resources, marketing (and public relations), finance, engineering, or any of many other specialized fields.
A consultant is usually an expert or a professional in a specific field and has a wide knowledge of the subject matter. The role of consultant outside the medical sphere (where the term is used specifically for a grade of doctor) can fall under one of two general categories:
Internal consultant - someone who operates within an organization but is available to be consulted on areas of specialism by other departments or individuals (acting as clients); or
External consultant - someone who is employed externally (either by a firm or some other agency) whose expertise is provided on a temporary basis, usually for a fee. As such this type of consultant generally engages with multiple and changing clients.
The overall impact of a consultant is that clients have access to deeper levels of expertise than would be feasible for them to retain in-house, and may purchase only as much service from the outside consultant as desired.