This is a structural material with cross section of 90 degree angle. The dimension is determined by the length and the thickness of the two sides. If the lengths of the two sides are equal, it is equal angle, otherwise it is unequal.
The sides are either equal or of different sizes, if one leg is longer than the other then it is known as UNEQUAL angle. It is used in all construction activity. The most common length available is between 10m to 12m.