A structured grid is one in which integration and intelligibility are arranged in a pattern of some kind, which supports functionality and intelligibility. Essentially, lines and areas are prioritised for integration and intelligibility to varying degrees in order to create a system of differentiation and it is this differentiation that we call structure in the system.
Hillier, B. (1996, 2007), Space is the Machine: A Configurational Theory of Architecture. Space Syntax: London, UK. pp.268-269