Manhattan distance
The Manhattan distance, also known as the L1-distance is the distance between two points measured along axes at right angles. In a plane with p1 at (x1, y1) and p2 at (x2, y2), the Manhattan distance is:
It is so named because it is the distance a car would drive in a city laid out in square blocks, like Manhattan (neglecting that in Manhattan there are one-way streets and some oblique streets).
L2-distance is called Euclidean distance.