Equip

Equip is a keyword ability found on artifacts with the subtype "Equipment". By paying the equip cost, you can attach the artifact to a creature, who is referred to in the text as the "equipped creature".

Description
Equipping can only be activated at sorcery speed. When an equipped creature leaves the battlefield, unlike Auras, the equipment remains on the battlefield.

The first cards with equip appeared in Mirrodin. It was so flavorful and so popular, that it went evergreen immediately. Ninth Edition was the first core set to feature the keyword.

Equip [quality]
Starting with Dominaria equip can now specify a quality a creature must have to be equipped.