If the graph is undirected, every entry is a set of two nodes containing the two ends of the corresponding edge; if it is directed, every entry is a tuple of two nodes, one denotating the source node and the other denotating the destination node of the corresponding arc.

As an example, the list {a,b},{a,c},{b,c} describes the undirected cyclic graph, where all three nodes a,b,c are connected to each other.

Typically, adjacency lists are unordered.