The angle symbols referred to in the crossword are known as Thetas. Theta is the eighth letter of the Greek alphabet and is used in mathematics and science to represent an angle or a rotation. It is also used in physics to denote an angular frequency, and in chemistry to denote an angle between two bonds. In geometry, it is used to denote an angle between two lines or planes. Theta is also used in trigonometry to denote an angle in a triangle.