In graph theory, centrality is any measure that determines how structurally important a node is within a graph and distance is measured by the number of hops it takes from get from one point to another. The shortest path distance between two nodes is the path that takes the minimum number of hops.
Closeness Centrality is a measure of a node's importance determined by the average shortest path distance from that node to every other node on the graph. The lower the average distance to all other nodes, the more central the position in the network.
An important thing to keep in mind when using Closeness Centrality is that this method treats each disconnected subgraph in a network as a separate graph. Be mindful that this will be reflected in the results. Harmonic Closeness Centrality resolves this issue by modifying the method for calculating the average shortest path.