this is referring to the idea that Rousseau pushed in his essay: 'The Social Contract' in relation to sovereignty.
Sovereignty is another word for saying who owns the political power. In an ideal world Rousseau felt that all people would be directly involved in the political process and that a 'general will' would emerge i.e. roughly what the people felt was the right thing to do. This would be achieved through debate and discussion amongst the people and then administrators would arrange for the policy the people had come up with, to be implemented.
This is of course the complete opposite of an authoritarian approach where power flows downwards from the leader. For Rousseau ideally it flowed upwards from the people to those hired to carry it out.
In practical terms it is impossible for all but the smallest communities (that is why we elect people to make decisions on our behalf) but that's what he advocated because he intensely disliked the authoritarian nature of Louis XV's regime, which was pretty similar to most regimes in Europe in the 1760s when he was writing.