visual angle

n. The size of a seen object measured by the number of degrees of the visual field through which it extends, which is determined by both the size of the object and its distance from the eye. As an instance, if you hold your thumb about 2.5 cm in front of your eye, your thumb will cover about 90 degrees of your visual field, whereas if you hold it at arm's length, it will cover around 1 degree of your visual field.