By angle:
We can classify a triangle 4 different ways when we're judging it by it's angle(s).
Acute: A triangle where all angles are less than 90 degrees.
Obtuse: A triangle where one angle is greater than 90 degrees.
Right: A triangle where one of the angles is exactly 90 degrees.
Equiangular: A triangle where all angles are the same (60 degrees.)
We can also classify a triangle by its sides:
Equilateral: (technically the same as an equiangular triangle, in order to have 3 equal sides you must have 3 equal angles as well.)
Isosceles: Two sides are the same length, where one is not.
Scalene: All three sides are different lengths.
I hope this helps!