You can see an interface as a contract that a class must meet: it
defines the methods, including the parameters and return values. For
a class to implement an interface it must implement all of the defined
methods exactly as defined. However, an interface is not limiting in
that a class can define other methods or the same methods with other
signatures.
Granted. I should've clarified that I was expanding on your .NET
definition. Marco is active in the PowerShell group so I'm
guessing .NET is what he's interested in.