What movement is called straight-line movement? What do the equations of this motion look like?

A straight line motion is a direction whose trajectory is straight. In straight motion, we can treat kinematic vector quantities as if they were scalar quantities x, v, and a.
A common assumption that relates to the many problems associated with straight-line motion is that acceleration is constant. With acceleration as a constant, we can obtain equations for the position, displacement and velocity of a particle or body experiencing rectilinear motion.