Pattern is a design principle - it is a repeated use of lines, colors, or other elements.
A familiar example is repeated dots in a piece of polka dotted cloth. Each dot is part of it.
Two-dimensional examples are created by using a motif over and over again. A motif is one complete unit in a larger design. A motif might be a simple flower-like design or a geometric shape used in a fabric decoration.
In three-dimensional art, a module is one complete unit. A brick is one kind of module. Others might be columns on a building or cylinders made of clay or a sculpture.
This design element tends to unify a work of art. When a motif or module is arranged regularly, the design is often called an "all-over" type.