A retainer fee is an established amount of money that a client pays to ensure the availability of a freelancer or an attorney, according to Entrepreneur magazine and About.com. Cornell University Law School explains three retainer fee structures for lawyers: general retainer, retaining fee and special retainer.
The law school says that a general retainer is for a set period of time, while a retaining fee is used to fund ongoing work. Money left over after the work's completion is returned to the client. A special retainer is for a project or case and is illegal in many states because it interferes with a client's right to fire her attorney.