Explain why a square is always a rectangle but a rectangle is not always a square.

A rectangle is a shape that has 4 sides and 4 90 degree angles, a square however has 4 equal sides, and 4 90 degree angles

It's like this: all chocolate cake is cake, but not all cake is chocolate cake. A square is a type of rectangle, but only squares can be squares, not all rectangles can be squares. Does that make sense?