Manhattan Distance is an alternative distance metric to Euclidean Distance. It is calculated by taking the absolute difference between two points.
Formally, it is given by:
$d_1(x, y) = \|x - y\|_1 = \sum\limits_{i=1}^{n} |x_i - y_i|$
As an example:
If $x = (a, b)$ and $y = (c, d)$ then:
Manhattan Distance = $|a - c| + |b - d|$