An interrupted grid is one in which all major lines, that is, the subset of the all-line map that constitutes the axial map, are either tangent to a vertex of a block or end on a block at close to ninety degrees. This means that lines either continue with or change in direction, or compel a ninety-degree change in direction.
Hillier, B. (1996, 2007), Space is the Machine: A Configurational Theory of Architecture. Space Syntax: London, UK. pp.276