The angle symbol, followed by three points that define the angle, with the middle letter being the vertex, and the other two on the legs.
So in the figure above the angle would be ∠ABC or ∠CBA.
So long as the vertex is the middle letter, the order is not important. As a shorthand
we can use the 'angle' symbol. For example '∠ABC' would be read as 'the angle ABC'.
Or like this: ∠B
Just by the vertex, so long as it is not ambiguous. So in the figure above the angle could also be called simply
Measure of an angle
The size of an angle is measured in degrees (see Angle Measures). When we say 'the angle ABC' we mean the actual angle object.
If we want to talk about the size, or measure, of the angle in degrees, we should say 'the measure of the angle ABC' - often written m∠ABC.
However, many times we will see '∠ABC=34°'. Strictly speaking this is an error. It should say 'm∠ABC=34°'
Types of angle
Altogether, there are six types of angle as listed below. Click on an image for a full description of that type and a corresponding interactive applet.