In this lesson, you use the word postation twice.

http://www.guitarmasterclass.net/ls/from-m...classical-pt-1/

Google doesn't turn up anything relevant.

/I need to start working on my singing, but I'm afraid my whole family will laugh while I practice.

First of all,don't be scared of practicing.Postation is more of a Italian or should I say european word.But I will explain to you how it works and what is the full meaning.Postation is position of your voice.So when you change your vocal position,your voice may sound like some is singing classical music,or metal or rock......etc.
So it is a difference in color,tone and every thing you voice is producing.