As carbon is in group 4 of the periodic table it has 4 electrons that it can share with other atoms to form covalent bonds. In the graphite structure, only 3 of these electrons are used for forming covalent bonds which means there is one free electron, which we describe as delocalised. Therefore, each carbon atom in graphite has a delocalised electron that can carry charge throughout the structure, which results in graphite conducting electricity.