In Guild Wars, to cover means to stack conditions, enchantments or hexes so that when they are removed, the more desired effects remain while the less important ones, the so-called covers, are removed. Skills used as covers are usually low cost and/or fast activating so that they can be quickly applied or re-applied.
Examples[ | ]
Using Apply Poison and Crippling Shot together will result in the poisoned condition covering the crippled condition. If only a single condition is removed, the cripple will remain, which is the more desired effect.
Using Spoil Victor before Parasitic Bond will result in Parasitic Bond covering Spoil Victor. If only a single hex is removed, Spoil Victor will remain, which is the more desired effect.