A rectangle is a shape with four sides and four corners, where opposite sides are equal in length. Squares are special rectangles. Children learn to spot rectangles in many everyday objects like doors, windows, and books.
A rectangle is a shape with exactly four sides and four corners. The corners are all square — they look like the corner of a piece of paper. The sides come in two pairs: the two long sides are the same length as each other, and the two short sides are the same length as each other. That is what "opposite sides are equal" means.
Look around the room. A door is a rectangle — two tall sides that are the same, and two shorter sides across the top and bottom that are the same. A window is a rectangle. A book, a table top, a piece of paper, a cereal box front — all rectangles. Rectangles are everywhere because the four-square-corner shape is very sturdy and easy to build with.
Here is something surprising: a square is actually a special kind of rectangle. It has four sides and four square corners, just like a rectangle — but all four sides are the same length. Every square follows all the rules for being a rectangle, so squares fit inside the "rectangle family." Not every rectangle is a square, but every square is a rectangle.
To check if a shape is a rectangle, count the sides (there must be exactly 4), check the corners (they must all be square), and check that the two long sides match each other and the two short sides match each other. If all of that is true, you have found a rectangle.
This is a foundational topic with no prerequisites.
No prerequisites — this is a starting point.