SVG filters provide many visual effects that correspond to effects found in bitmap graphics packages. An SVG filter is defined within the defs element and is referenced from an element within the main part of an SVG document.
SVG filters are defined using a filter element within which are nested one or more elements that describe filter primitives. A filter primitive can be seen as a component of a filter effect. For example, when a drop shadow is created, it is typically also offset. In SVG, that class of filter effect is created using an feGaussianBlur filter primitive, an feOffset filter primitive, and an feMerge filter primitive.