Closeness centrality is a measure used in network analysis to determine how close a node is to all other nodes in a graph. It is calculated by taking the inverse of the sum of the shortest paths from a node to all other nodes. A higher closeness centrality indicates that a node can reach other nodes more quickly, making it more influential in spreading information or resources. This concept is often applied in various fields, including social networks, transportation systems, and epidemiology. For example, in a social network like Facebook, a user with high closeness centrality can connect with many friends quickly, enhancing their ability to share content or mobilize support.