RECTILINEAR MOTION - When an object in translational motion* moves in a straight line, it is said to be in rectilinear motion. Examples are a car moving on a straight road and a train moving on a straight track.
CURVILINEAR MOTION - When an object in translational motion* moves along a curved path, it is said to be in curvilinear motion. Examples are a stone thrown up in the air at an angle and a car taking a turn.
*translational motion is a type of motion in which all parts of an object move the same distance in a given time.