<p>What is and how can it be used in C#.<br/>
Can you use the same concept in Python/Perl?</p>

A
partial type
(it doesn't have to be a class; structs and interfaces can be partial too) is basically a single type which has its code spread across multiple files.
The main use for this is to allow a code generator (e.g. a Visual Studio designer) to "own" one file, while hand-written code is put in another.
I've no idea whether Python/Perl have the same capabilities, I'm afraid.