Anyone knows slang/alternative words for Freelance, Freelancer or Freelancing in general?

Many publications, including newspapers and magazines, designate nonsalaried non-staff writers as "contributors."

In newspaper terminology, a freelance news reporter is a "stringer."

In other functions, freelancers are often simply referred to by the type of work they contribute--e.g. "illustrator," "columnist," "photographer," "news writer," etc. If it is necessary to distinguish these from full-time staff, you could say "contributing photographer," etc.

well i know that a freelance and possibly a freelancer is a type photographer

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In industry you generally call them a contractor.

Free agent, self-employed, unaffiliated, independent.

freelicious, freelegal