Steel angles are L-shaped sections with plenty of uses, the main ones of which are typically constructional. 
 
It is easy to work with and relatively easy to cut, as well as to weld, and all of this makes it a popular format for steel for the construction industry.
Angle steel may particularly be seen in the construction of frames and racks, as well as any other application for which it is suited.
When specifying angle steel, there are two main options: equal angles and unequal angles.
This is actually not to do with the size of the angle between the two sides, which is fixed at 90 degrees; instead, it relates to the ratio of the length of the two sides.
In an equal steel angle, the sides – think of them as the two strokes of a capital letter L – are of equal size, hence the name.
Equal steel angles start from 40mm x 40mm and range up as far as 200mm x 200mm, in a range of thicknesses from 4mm to 24mm.
Unequal steel angles have two different measurements for the sides, ranging from 65mm x 50mm to 200mm x 150mm.
The ratio between the two may vary, and again a variety of thicknesses are available to suit different applications.