To describe the motion of an object, one should first be able to describe its position (where it is at any particular time). More precisely, the position needs to be specified relative to a convenient frame of reference. A frame of reference is an arbitrary set of axes from which the position and motion of an object are described. Earth is often used as a frame of reference to describe the position of an object in relation to stationary objects on Earth.
Further, several important kinds of motion take place in two dimensions only—that is, in a plane. These motions can be described with two components of position, velocity, and acceleration. If an object moves relative to a frame of reference, then the object's position changes; this change in position is called displacement. The word displacement implies that an object has moved or has been displaced. Since displacement indicates direction, it is a vector and can be either positive or negative, depending on the choice of direction. Also, an analysis of motion can have many displacements embedded in it, and many applications in physics can have a series of displacements. Thus, the total displacement is the sum of the individual displacements, which should be evaluated carefully using vector addition.
This text is adapted from Openstax, University Physics Volume 1, Section 4:1 Displacement and Velocity Vectors.
