To a biologist, the term quorum sensing in nothing new. Perhaps it is familiar to all, but just in case, Wikipedia article on it is very nice and detailed. Let me define it nonetheless: quorum sensing has nothing to do with voter turnout or voting machines, it is a particular phenotype, or behavior, that certain living organisms begin to show when their population reaches a certain density in a certain environment -- such as bacteria in a carton of milk, for example. This threshold of "crowdedness" of bacterial individuals in a milk carton is called a quorum. Apparently, they have a way of knowing that they reached a quorum: they sense it (and there is nothing mysterious as to how -- they have ways, and the point of the story is not about those ways).
At any rate, having sensed the quorum, bacteria begin to display a new behavior, or activity.