A triangle where all three sides are different in length.

Try this Drag the orange dots on each vertex to reshape the triangle.
Try to establish a triangle that is not scalene. Sometimes called an irregular triangle.

Scalene triangles are triangles where each side is a different length.
They are unusual in that the are defined by what they are not. Most triangles drawn at random would be scalene.
The interior angles of a scalene triangle are always all different.
The converse of this is also true - If all three angles are different, then the triangle is scalene,
and all the sides are different lengths.

Scalene Triangle Facts

Interior angles are all different

To see why this is so, imagine two angles are the same. The triangle would then be an Isosceles triangle,
which has two sides the same length. Similarly, if all three angles are the same, it would be an equilateral triangle
and all three sides would be the same length. See the entries for
Isosceles and
Equilateral triangles.

Since in a scalene triangle you probably know the lengths of all three sides,
the best way to calculate the area is using Heron's Formula.
However you can use any method that works with what you are given. See Area of a Triangle