Is a square always sometimes or never a quadrilateral?

A quadrilateral always has four sides.
A square always has four sides
→ a square is always a quadrilateral.

A quadrilateral's only distinguishing feature is a shape with four sides.

A square has four sides, but also those four sides must all be the same length and all the angles are the same, at 90o.

So squares are always quadrilaterals, but quadrilaterals are only sometimes squares.