Drop
From Guild Wars Wiki
When a party kills a creature, it can drop loot in the form of items or gold. Items are assigned to a single member of the party (including heroes and henchmen, in which case the item is never seen), but gold is shared equally between all party members in the instance (including heroes and henchmen, and allied parties in multi-party missions) upon being picked up. Normal foes can generally only drop a single item or item stack, while bosses can drop up to five items. Quest item and festival item drops are independent of normal drops and can cause additional drops to come from a single kill. Ownership of an unclaimed drop expires after 10 minutes.
Some players argue that killing an entire mob of enemies instead of just one or two will lower the drops/drop rate if they die at the same time.
Opening a chest or interacting with treasure will also result in loot being dropped.
