What is preserving baseband? Do i need to do that?

I was thinking of jailbreaking my iphone to ios 6.1.
My iphone 3gs is right now running on jailbroken ios 4.1

You must download and install the latest version of the QT, QT Mobility and QT webing…

I think baseband is something like urm… A model number, different versions are put out in stores over time as apple "patch", and jailbreaks have to be compatible with it.
but then again i'm pulling this out my ***, but I have heard the word before and this is what comes to mind.

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