All nodes have 1, 2 or 3 value(s) and 2, 3 or 4 child nodes. • If a node has 1 value, the node has 2 child nodes, and so on. • A node which has N child nodes is called N-node. • For each node, the values in the nodes and its descendants are ordered. x < A A B A < x < B B < x A 3-node and its descendants 8