Physics is the study of movement and change. One of the major topics is the movement of objects. One type of movement is in two dimensions. This refers to objects that move forward and/or backward. This is commonly called the x direction. The second dimension is the up/ down direction or y direction.
Other types of two dimensional motion include relative motion and uniform circular motion also. Relative motion refers to an object move relative to another . An object that moves in a circle at a constant speed is in uniform circular motion. An example would be clothes in a washer.
Below are resources for more information on two dimensional motions and physics.