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, human resources, marketing (and public relations), finance, engineering, science 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: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.