What does NaN mean? How do you fix this?

Hello, I'm having trouble with my coding. Upon clicking on a button I would like my movie clip to appear and subtract 1 from my variable. My variable is called 'woo'. My movie clip is called 'mydays'. Here is the code:

Code:

---

on (release) {
        if (_root.mydays._visible) {
                _root.mydays._visible = false;
        } else {
                _root.mydays._visible = true;
        }
}
on (release) {
        if (day < 30) {
        day += 1;
        hp += 50;
} else if (day = 30) {
        gotoAndPlay ("endofgame")
}
}

on (release) {
        _root.mydays. woo -= 1;
}

---

Every time I test my button, my movie clip appears as I want it to but the variable says NaN. What does this mean? How can I fix this?

NaN means "not a Number".
Is your variable inside your MC??
Can´t understand this code.
Attach the file.

You need to assign a number to a variable before you try to use it in math.

Code:

---


_root.mydays.woo =100;


on (release) {
        if (_root.mydays._visible) {
                _root.mydays._visible = false;
        } else {
                _root.mydays._visible = true;
        }
}
on (release) {
        if (day < 30) {
        day += 1;
        hp += 50;
} else if (day = 30) {
        gotoAndPlay ("endofgame")
}
}

on (release) {
        _root.mydays.woo -= 1;
}

---

Yes my variable is inside my movie clip. The file is too big for me to attach it.

Never mind, I figured out what was wrong. Thanks for helping!