Pattern
A repeating structural motif, distinguished from plain Repetition by having its own internal modular logic.
In practice
A pattern is a repeating motif built on its own internal logic: a unit plus a rule for how it repeats, such as a mirror flip, a rotation or a half-step offset. Because of that logic it can cover any surface seamlessly. Wallpaper, textile prints and the tiled background on a brand's packaging are typical patterns; designers check them for visible seams and for unwanted stripes that appear from a distance.
Often confused with Repetition
A pattern has its own internal logic of arrangement; repetition is the simpler case of one element recurring evenly without variation.
Try this
Draw one simple motif on a square, then tile it four ways: straight, flipped, rotated and offset.