It is based off of the angles of the triangle and the sides.
A triangle with a right angle (90°) is a right triangle.
A triangle with an angle larger than 90° is an obtuse triangle.
A triangle with angles that are smaller than 90° is an acute triangle. ALL ANGLES MUST BE SMALLER THAN 90°...
With sides, if a triangle has two angles that equal the same length, it is an isosceles triangle.
If NO sides are of equal length, it is a scalene triangle.
And if ALL sides are equal, then it is a equilateral triangle.
