The radius attribute represents the radius (or radii) for the operation on a given <feMorphology> filter primitive.
If two numbers are provided, the first number represents the x-radius and the second one the y-radius. If one number is provided, then that value is used for both x and y. The values are in the coordinate system established by the primitiveUnits attribute on the <filter> element.
A negative or zero value disables the effect of the given filter primitive (i.e., the result is the filter input image).
You can use this attribute with the following SVG elements: