Feeder literally means a person or thing that supplies food or feeds something or someone. But when it comes to BBW or plus-size hookups, feeder means folks who love to feed BHM and BBW. Although it sounds like a connotation for many people, it depends on how people perceive the definition. It is a sexual orientation.
The feeder can be a regular guy or woman who feeds the other one to attain various weight goals. In most cases, the feeder expects overweight results from other parties since they are fat admirers or fans.