Well, I just guess I'll have to define it my own self:

Negative harmony is the requirement that if a verb is negated in a sentence then either the subject or the object or both must also be negated, Examples

English - I ain't got no money

Spanish - No hay nada 'There isn't nothing.'

Russian - Я не знаю. Я ничего никогда не знаю. 'I don't know. I don't never know nothing.'