Sometimes you want blur you background hdri, so it is not distracting too much. Blender comes with no blur node. But you can create such in simple way, although it is recommend for ease of use to download and reuse premade nodes group.
Please follow short tutorial to learn more:
Blur hdri or any other texture in Blender – nodes scheme
You can also try to recreate it on your own from the scheme, but don’t forget to save it for later use as a node group.