Item container

 (or loot containers or drops) have a chance of appearing after defeating an enemy in space combat or ground combat. They can be interacted with to take the item(s) so they are stored in the inventory.

These containers differ in shape according to the rarity of the item(s) within, providing a visual reference to the player to recognize items of greater rarity and thus higher value.

When you are in a group, loot will be distributed according to specific loot settings.

and level items don't drop so they don't have a special container.

Lock Boxes container
These are pictures of Lockboxes post-Agents of Yesterday launch. Before this they had a white light (like the one found on common item drops) shooting out of them.