Right angle is a very important concept in the area of mathematics, on the basis of right angle concept whole of advanced geometry is built (Trigonometry).

So whenever you are in need to calculate the heights of building or dealing with inclined planes we make use of Pythagorean right angled triangle.It consists of perpendicular distance, an inclined plane and a base.  

A right angle is an angle whose degree measure is 90º.
Right Angle

In the above diagram angle B is marked as 90º and hence it is a right angle. The box symbol ⌉ represents the right angle and indicates the angle measure is 90º. The two intersecting rays AB and BC are said to be perpendicular to each other.

In general lines that intersect to form right angles are perpendicular.
If the side CB is extended to CD, the angle formed ABD is also a right angle.
Right Angle on Both Sides
The supplementary angle of a right angle is also a right angle.

Indeed when two perpendicular lines intersect, they form four right angles around the point of intersection.

Four Right Angles

Unlike acute and obtuse angles all right angles are congruent as all of them measure 90º.