Shortest path is defined in terms of how distance is conceptualised in a model of human navigation. It can be interpreted as least length path (the shortest metric distance), fewest turns path( the least number of direction changes), or least angle path (the smallest accumulated total of angular change on the path between origin and destination).
Hillier , B. & Iida, S. (2005), Network and psychological effects in urban movement, In: A.G. Cohn and D.M. Mark (Eds.): COSIT 2005, LNCS 3693, pp. 475-490.