A consultant (from the Latin consultare means ""to discuss"" from which we also derive words such as consul and counsel) is a professional who provides professional or expert advice in a particular area of expertise such as management, accountancy, the environment, entertainment, technology, law, human resources, marketing, emergency management, food production, medicine, finance, life management, economics, public affairs, communication, engineering, sound system design, graphic design, or waste management. 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.