Whats an Alias?

I'm connected to my network at my halls. When I open my "Macintosh HD" and then click on Network up comes a couple of folders. When I click on them I can see lots of files with the grey sphere icon named with what I can only assume are the names of peoples computers on the network.

For alot of them when I click the connect button it comes back with an error saying "The alias...could not be opened, because the original item cannot be found" what does this mean?

What’s the Library file that’s there. This file is always on every network that I join but I can never open it because guess what, the alias could not be found.

Alias's are like shortcuts in windows. It shows the name of a file/drive/computer but is just a reference to the actual item