What is rectilinear motion or translatory motion or translational motion or one dimensional motion

.In such motions the position given by only one of the three cartesian co-ordinates i.e., x or y or z changes with time, e.g.,
(i) A fruit falling from a tree.
(ii) A train running on a straight railway line.

(iii) A car running on a narrow straight road etc. Vi In the given figure a particle moves from origin along x-axis so it co-ordinate changes from O to x1