All the angles of a quadrilateral are equal. What special name is given to this quadrilateral?

According to the question,

If the angles of a quadrilateral are equal, then it is a rectangle .

This can also be seen here as follows:

Suppose all the angles of the quadrilateral = x

We know that, Sum of all angles of a quadrilateral = 360°

⇒ x + x + x + x = 360°

⇒ 4x = 360°

⇒ x = $\frac{{360}^{\mathrm{o}}}{4}$

⇒ x = 90°

Hence, the quadrilateral is a rectangle.

A square also has all the angles of measure 90°, but since no information about the sides are given in the question , the correct answer would be recangle.