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+.. _guide-graph-basic:
+
+1.1 Some Basic Definitions about Graphs (Graphs 101)
+----------------------------------------------------
+
+:ref:`(中文版)<guide_cn-graph-basic>`
+
+A graph :math:`G=(V, E)` is a structure used to represent entities and their relations. It consists of
+two sets -- the set of nodes :math:`V` (also called vertices) and the set of edges :math:`E` (also called
+arcs). An edge :math:`(u, v) \in E` connecting a pair of nodes :math:`u` and :math:`v` indicates that there is a
+relation between them. The relation can either be undirected, e.g., capturing symmetric
+relations between nodes, or directed, capturing asymmetric relations. For example, if a
+graph is used to model the friendships relations of people in a social network, then the edges
+will be undirected as friendship is mutual; however, if the graph is used to model how people
+follow each other on Twitter, then the edges are directed. Depending on the edges'
+directionality, a graph can be *directed* or *undirected*.
+
+Graphs can be *weighted* or *unweighted*. In a weighted graph, each edge is associated with a
+scalar weight. For example, such weights might represent lengths or connectivity strengths.
+
+Graphs can also be either *homogeneous* or *heterogeneous*. In a homogeneous graph, all
+the nodes represent instances of the same type and all the edges represent relations of the
+same type. For instance, a social network is a graph consisting of people and their
+connections, representing the same entity type.
+
+In contrast, in a heterogeneous graph, the nodes and edges can be of different types. For
+instance, the graph encoding a marketplace will have buyer, seller, and product nodes that
+are connected via wants-to-buy, has-bought, is-customer-of, and is-selling edges. The
+bipartite graph is a special, commonly-used type of heterogeneous graph, where edges
+exist between nodes of two different types. For example, in a recommender system, one can
+use a bipartite graph to represent the interactions between users and items. For working
+with heterogeneous graphs in DGL, see :ref:`guide-graph-heterogeneous`.
+
+Multigraphs are graphs that can have multiple (directed) edges between the same pair of nodes,
+including self loops. For instance, two authors can coauthor a paper in different years,
+resulting in edges with different features.