Freelance Worker - (noun)
A freelance worker, also known as a freelancer, is someone who works on a contract basis for a variety of companies, and not as an employee for a single company. They are often considered to be self-employed.
Source: Adapted from BusinessDictionary
Example of Use: It can be difficult for freelance workers to put together a resume as they may have no single prior employer and their work is often short in duration.