A recurring fee that reserves a professional's time or guarantees ongoing work each month, paid whether or not the full time is used.
A retainer flips the freelance relationship from project-based to subscription-based: the client pays a fixed monthly fee, and the professional guarantees availability, a set number of hours, or a defined bundle of ongoing work.
For buyers, retainers buy priority — your work doesn’t wait behind other clients’ projects. For sellers, they buy predictable revenue, which is why many offer a discount versus their project rates.
The two things every retainer agreement should define: what happens to unused time (does it roll over, expire, or get partially credited?) and what counts as in-scope versus billable extra. Retainers without those definitions turn into arguments by month three.