Every Culture is reliant on several types of Infrastructure to keep running. The exact types depend on the sort of Culture you're building and the individual location in question. These infrastructure types are the background maintenance costs of running a Culture. Usually they are a type of demand that is generated by population and buildings and supplied by other buildings and certain technologies (though some certain other technologies will increase the need for infrastructure as well). By keeping the Culture's infrastructure running well you will be able to have your Culture operate at full capacity.