Literally 'piecemeal selling principle'; a euphemistic or critical term for prostitution, emphasizing the selling of one's body in parts.
She fell into prostitution out of poverty.
The standard, neutral term for prostitution. 切り売り主義 is a much rarer, more literary or critical expression.
Compound of 切り売り (piecemeal selling) + 主義 (principle, doctrine). The exact origin is uncertain; it is a figurative expression for prostitution.