Co-linked

Source: Yugioh Wikia

A co-link in a link between 2 Link Monsters where each monster have Link Arrows that point to each other.

A series of co-linked Link Monsters that connects one Extra Monster Zone to the other is known as an Extra Link. All monsters involved in this series are Extra Linked, which is a particular kind of being linked. Any monster co-linked with an Extra Linked monster is also Extra Linked.