Adjacency refers to the state of being next to or adjoining something else. In various fields, such as mathematics and geography, it describes how objects or areas are positioned in relation to one another. For example, in a grid, two squares are considered adjacent if they share a side. In computer science, adjacency often relates to data structures like graphs. In a graph, two vertices are adjacent if there is a direct connection or edge between them. Understanding adjacency is crucial for algorithms that traverse or analyze these structures, such as search algorithms.