I am just learning the guitar, and I'm starting on an acoustic. I'm still trying to figure everything out. I have only been messing around with tablature(tabs only so far, no notes yet), and I'm trying to teach the tabs to myself, along with teaching the guitar to myself too. I've been figuring out tablature pretty good, better than I'd predicted anyway. The only thing that has me held up are the X's that are in with the fret numbers on tabs.. For Example: On a tab I was looking at earlier, the first line of tablature in the Intro under E5 read: (from e-E) (0-0-x-2-2-0)... So far I have just been playing the X's as an open chord, but then I came across the tablature I used in the Example("Where Did You Sleep Last Night", Nirvana's version), and it was the first time I have seen one of the x's directly below, or directly above a 0 in the same vertical line of tabs, and now I'm sorta stumped.. My problem is that I've always thought that a 0 was the symbol to play that certain string Open, and if 0 does in fact mean Open, then what does an X mean?

Much appreciation to anyone who may be able to help.. Thanks ahead of time.. Peace.
X means do not play the string.
Lightly press a fretting finger on the string to mute it so it doesn't ring out.

Gibson 2005 Les Paul Standard
Fender Road Worn Strat w/ Noiseless pickups
Marshall JCM 2000 401C
Marshall Vintage Modern 2266
Marshall 1960A cab (Dave Hill from Slade's old cab)
Ibanez TS9DX
EHX Little Big Muff
Freshman Acoustic
hit the string, but mute it so that it doesn't sound
But boys will be boys and girls have those eyes
that'll cut you to ribbons, sometimes
and all you can do is just wait by the moon
and bleed if it's what she says you ought to do