A retainer fee is an upfront cost paid to a professional, such as a lawyer or consultant, to secure their services for a specific period. This fee ensures that the professional is available to work on the client's needs as they arise. It is often used in legal and business contexts to establish a working relationship. The retainer fee may cover a set number of hours or services, and any additional work may incur extra charges. Clients typically receive regular statements detailing how the retainer is being used, allowing for transparency in the billing process.