It is a right angle you guys are stupid if you do not know that.
a 3 sided shape is a right angle triangle
A right angle triangle
an angle with a acute and right angle
A right angle triangle
a right angle triangle.
a right triangle
If a shape has four sides and you know that it has one right angle, yet you do not know anything else about the shape, then the most specific geometric term you can assign to the shape is "quadrilateral". Unless you know about the other angles and side lengths, nothing more can be said.
an obtuse angle
L
a cube
A right angle triangle