Question: In Eclipse, what is a "Package" explained in .NET terms?

Answer: 
A package in java is most comparable to a namespace in .NET.

EDIT:

As pointed out by R0MANARMY, in Java the folder structure & where classes are dictate which package they belong to. In .NET classes can be marked as belonging to any namespace regardless of the folder they are in.
A Java package is something like a namespace in .NET