Is a rhombus a square

Sometimes, but not every time.

A rhombus can be a square, but it doesn't always have to be.

A square is a rhombus that has special, extra requirements ...

its angles must be 90°. So every square is a rhombus, but

not every rhombus is a square.

A rhombus is a quadrilateral in which all of the sides have equal length.

A rhombus can be a square sometimes if the angles are 90 °.