As it sounds, it is breastfeeding for pay. Erotic lactation is considered a taboo by many because of its proximity to incest and children. "Milk fetishism" and "lactophilia" are medical, diagnostic terms for paraphilias and are used for disorders according to the precise criteria of ICD-10 and DSM-IV.
In 2003, there was a report of New Zealand brothel that offered lactation services to its clients. Though not strictly prostitution, a Beijing restaurant offered breastmilk-based dishes on its menu.
Donna is a lactating whore who works in a house that caters to fetishes such as infantilism.