it's a day of the week, sometime between wednesday and saturday, but not necessarily thursday or friday. it changes, and it's not every week. it doesn't have anything to do with drinking light beer.
cody:hey yona, sup?
yona: not much, you?
cody: well, last naturday, i beat fallout 3
yona: naturday? what the hell?
cody: yeah, naturday, it's a day between wednesday and friday