This is the most standard blur: the more you increase its size, the less the sharp and angular areas of the source image will be visible. It may also be applied only to the transparency channel of the image (alpha channel).
After applying the blur :
The Blur > Gaussian Blur effect
An image with a Gaussian Blur may be compared to an image seen through a camera that is not set correctly.
The Gaussian Blur is more precise than the Cubic Blur.
The Blur > Center Blur effect
We studied the Center Blur in detail in lesson 12 about the FX stack concept. The parameters are the position of the center, the power of the blur and the radius of the circle.