[Newbies] How do different "package"-like things relate

[itsme213]

I see package-like things in many places:
- Universe Browser
- Monticello Browser
- SqueakMap Browser

Do all these have the same notion of a package, and the same source for 
their packages? I am a bit confused because I see some "package"-like 
instances in one browser that don't seem to match what I see in the others.

Thanks.