Graph is a collection of points and lines connecting some subset of them. In space syntax, the points of a graph denote spaces (e.g. streets, rooms or corridors), and the lines represent intersection between pairs of the spaces.
Graph
Sources
Hillier, B., Hanson, J., and Graham, H. (1987), Ideas are in things: an application of the space syntax method to discovering house genotypes. Environment and Planning B: Planning and Design, v14, 363-385. pp. 363-4.