What is called Light travels in straight line?

Answer 1

A geodesical path

Answer 2

Sort of. Technically light travels in what's called a geodesic curve, which is the straightest possible line given the local curvature of space. In empty space, that's a straight line. Near a massive object, it's not a straight line.

Answer 3

The principle that light travels in a straight line is known as the law of rectilinear propagation. This law states that light rays move in a linear path unless they are affected by an obstacle or medium that causes them to deviate.