A right angle is the name given to a quarter of a turn and
is equal to 90^{o}. It is the angle between vertical and horizontal,
the angle between north and west.

In geometry and trigonometry, a right
angle is an angle of 90 degrees, corresponding to a quarter
turn (that is, a quarter of a full circle). It can be defined
as the angle such that twice that angle amounts to a half
turn, or 180^{o}.

Many instruments have been designed
to draw a right angle, such as a set square and T-square,
because of its importance in construction and building.

In
mathematical drawings, a right angle is indicated by a small
box. Lines that are at a right angle to each other are perpendicular,
an important geometrical property. The presence of a right
angle in a triangle is the defining factor for right triangles.

The word angle comes from the Latin word angulus, meaning
a corner. The word angulus is a diminutive, of which the primitive
form, angus, does not occur in Latin.

Example of a Right Angle: