Rooting an android device?

I am very new to android devices, however I have heard about rooting my device. It was not explained to me what it was and im usually told "if you dont know what it is, dont worry about it" I would at least like to know what it is. Is it similar to ssh-ing an idevice? Is it an advanced way of personalizing my device? Please help! (i am on a samsung galaxy tab)