There are no squares in nature
Air conditioning vents
Rubik's cube sections
Slices of bread
Board games (checker board, chess board, etc)
Tiles (scrabble, floor/backsplash)
Laundry shute/garbage shute door
Crosswalks at intersections
Synonyms: boxy, equilateral, quadrate, quadratic, right-angled, squarish, four-sided
Describing a shape is best done in as few words as possible. Think of the shape as a camera snap shot--you want to capture the gist of what you mean as soon as possible so you can get on with other related (and more important) detail, and the action happening in the scene
A weak example:
I frowned at the brownies I'd dished up for my company. The squares looked so uninteresting against the shiny white plates.
What's wrong with this example?
It's simple--squares are, well...boring. They can't stand alone as a descriptior for contrast or comparision. More detail is needed to make the description stay with the reader.
A strong example:
The rain pattering the roof woke me from my afternoon nap and I stretched, cat like, wondering what time it was. A glance at the wall clock showed noon had long since passed. I shot up and ran for the front door, praying that I wasn't too late...but I was. There lying on the rain-drenched step was my long-awaited Fed Ex envelope, soggy and limp as a grungy dish rag.
Why does this work?
This one works because shape and texture are both utilized to not only describe the item but to also accurately describe its condition.