A feeder is someone (usually a human) who willing give blood for Moroi survival.
A Quote From Vampire Academy: The Ultimate GuideEdit
Feeder: "A human who willingly donates blood to a Moroi. Feeders usually become addicted to the drug-like endorphins in a vampire's saliva, which give intense pleasure when bitten."
Usually, Strigoi kill when they feed, but for their own torturous reasons, some Strigoi will keep humans, dhampirs, or some Moroi captive and use them as feeders.
When Rosemarie Hathaway, Mason Ashford, Eddie Castile, Mia Rinaldi, and Christian Ozera were captured and held captive by Strigoi Isaiah and Elena, Isaiah would stop by every so often and take a drink from Eddie. Eddie was left scarred by the incident and blames himself for everything.
Strigoi Forced Feedings in Shadow KissEdit
When St. Vladimir's Academy was attacked by Strigoi, some Moroi and Dhampirs were taken captive. While they were in a cave about five miles from the school, the Strigoi used some of the people as feeders.
Strigoi Not-So-Forced Feedings in Blood PromiseEdit
When Rosemarie Hathaway was searching for lover and awakened boyfriend, Dimitri Belikov, in Russia, he captured her and held her captive. While he did, he was feed from her every so often to keep her reasonable side muddled in bliss so there was no way she could plan escape.