Which of the following parts of the blur dialog box refers to the overall size of the blur?

The "Radius" setting in the blur dialog box specifically refers to the overall size or extent of the blur effect applied to an image or a portion of it. This parameter determines how far the blur extends from the edges of the focused area. A larger radius results in a more pronounced blur effect, affecting a wider area, while a smaller radius restricts the blur to a tighter area around the focal point.

In contrast, intensity relates to the strength of the blur effect but does not specify its size. Gradient typically describes how the blur transitions from clear to blurred but does not directly indicate the overall size. Opacity refers to the transparency of the image and does not influence the blur size at all. Thus, "Radius" is the correct term associated with overall size when applying a blur effect.