this type of employee is someone who does work for an organization on a temporary or part-time basis
Temporary work Temporary work or temporary employment refers to an employment situation where the working arrangement is limited to a certain period of time based on the needs of the employing organization. Temporary employees are sometimes called "contractual", "seasonal", "interim", "casual staff", "outsourcing", "freelance"; or the word may be shortened to "temps". In some instances, temporary, highly skilled professionals (particularly in the white-collar worker fields, such as law, engineering, and accounting) refer to themselves as consultants.