Networks are interconnecting subjects, people, elements or things. They can be displayed graphically.
Network theory is "the study of a set of techniques for the analysis graphs." - University of Cambridge, Department of Computer Science and Technology
Network analysis is "the process of measuring movements of information in various parts of a network." - Cambridge Dictionary
Nodes are the subjects, people, elements, or things in a network.
Edges are the links or connections (drawn as a line or arrow) between nodes.