Temporary help is sometimes used to refer to administrative rather than technical personnel, usually hired from an agency. These requirements come from past big-name scandals in which money was funneled to individuals for unspecified services. Avoid this by always including a statement of work that specifies the nature of the services to be provided. With no standard terminology, there is no reason why you cannot think of Henry Kissinger as temporary help, and no reason why a janitor cannot bill himself as a consulting sanitation specialist. One may obtain consulting services directly from an individual, through a consulting company, or through an agency.
Individuals often operate with the least overhead.
A consulting company provides a range of professional skills, equipment, support staff, and takes responsibility for the work of its staff. An agency provides marketing services for individuals, but no technical support. The federal government and most states have rules about the distinctions between employees and consultants aimed at requirements for tax withholding, disability insurance and the like. Hiring through a corporation minimizes these problems, at a cost. Few technical consultants just give advice, although giving advice is one aspect of many jobs.