The eigenvalues of a graph are defined as the eigenvalues of its adjacency matrix. The set of eigenvalues of a graph is called a graph spectrum. The largest eigenvalue absolute value in a graph is called the spectral radius of the graph, and the second smallest eigenvalue of the Laplacian matrix of a graph is called its algebraic connectivity. The sum of absolute values of graph eigenvalues is called the graph energy.

algebraic connectivity | characteristic polynomial | cospectral graphs | graph energy | graph spectrum | spectral radius