consultant

A consultant (from "to deliberate") is a professional (also known as expert, specialist, see variations of meaning below) who provides advice or services in an area of specialization (generally to medium or large-size corporations). Consulting services generally fall under the domain of professional services, as contingent work.

The Harvard Business School defines a consultant as someone who advises on "how to modify, proceed in, or streamline a given process within a specialized field".