1 [data models] A line between two points that forms a boundary. In a geometric shape, an edge forms the boundary between two faces. In an image, edges separate areas of different tones or colors. In topology, an edge defines lines or polygon boundaries.
2 [network analysis] In a network system, a line feature through which a substance, resource, or traffic flows. Examples include a street in a transportation network and a pipeline in a sewer system. In a geometric network, a network edge can be simple or complex. A simple edge is always connected to exactly two junction features, one at each end. A complex edge is always connected to at least two junction features at its endpoints, but it can also be connected to additional junction features along its length. In a network dataset, a network edge is only connected to two junctions at its endpoints.
3 [3D analysis] In a TIN data model, a line segment between nodes (sample data points). Edges store topologic information about the faces that they border.