Binary tree is a specialization of Graph data structure. Node in a Graph is called a Vertex and the connection between two vertices is called an Edge.
If we use this terminology, A Binary tree edge is only from a parent to its (at the most two) children. In Graph, any vertex (Node) can connect to any vertex and there is no limit on the number of vertices that a vertex can connect to. The connection can be uni-directional (as in Binary trees) or bi-directional. When connections are uni-directional the edge is called directed edge and graph is called directed graph. When connections are bi-directional, edge is called un-directed edge and graph is called undirected graph. Because of these connections, there is no hierarchy among the vertices of a Graph.