Instances

Yes mostly. But when you do it from the Shift + A menu, you can instance a collection with whatever is in it. 

You got it! I often say "instance" instead of "object with linked mesh data" because the latter doesn't exactly roll off the tongue, but Omar is right that there are also collection instances. You can just think of them as object instances and collection instances, but you probably don't need to worry about collection instances at this point in the journey.