Is a rectangle a square?

It could be.

A square is always a rectangle.

Well a square must have 4 equal sides. A rectangle doesn't have to.

Following on from Ms. Sue,

While you can say a square is always a rectangle, a rectangle isn't always a square.

they are both quadrilaterals so maybe. hope this helps.:)

Ah, but while all rectangles and squares are quadrilaterals not all quadrilaterals are squares or rectangles.

No, a rectangle and a square are two different shapes. While both have four sides and four angles, a rectangle has opposite sides of equal length, but its angles can be any value (except for 180 degrees). On the other hand, a square is a special type of rectangle where all four sides are equal in length, and all four angles are right angles (90 degrees). So, every square is a rectangle, but not every rectangle is a square.