What is the name of alien which has four arms?

There is no single, specific alien species with four arms that has a widely recognized name.

However, there are many fictional alien species with four arms, including:

* The Xylons from "The X-Files"

* The Sontarans from "Doctor Who"

* The Quadlings from "The Wizard of Oz"

* The Zerg from the "StarCraft" series

* The Twi'lek from the "Star Wars" universe

* The Na'vi from "Avatar"

It's important to note that these are just a few examples, and many other fictional aliens with four arms exist in different media.

If you're looking for a specific alien with four arms, you'll need to provide more context or information about where you encountered it.