I've been seeing those terms a lot lately, particularly in questions and comments concerning Witchcraft. I see people say, "Are you a good Witch or a bad Witch?" like this is the Wizard of Oz or something, and then see comments like, "I practice only white magick. I don't want to mess with black magick." Then there's the "Left Hand Path," and "Right Hand Path," stuff. I understand that some people just feel more comfortable using these terms, for whatever reason, but more often than not, it seems as though the Witch saying these things is using them in an attempt to "justify" his or her beliefs. Personally, I think they all sound silly and aren't very accurate.
First of all, Magick is neither good nor bad, white nor black, etc. It just IS. It's there, it can be used, and the Witch using determines the path it takes, whether it's for positive use or negative.
So what is positive magick and negative magick? Positive magick is for the good of all, or at least for the good of some with no harm to others. Positive magick includes things like healing. Positive magick is life affirming, always. Negative magick is magick that causes negativity for anyone or anything (manipulative magick, magick to control another person, magick to intentionally harm another person, etc.), from attempting to mess with someone's free will in some way to intentionally causing them harm. Even if your work seems to be positive, you need to examine it carefully. Pay attention to the words you use. Just because something is good for you, doesn't mean it will be good for me, or anyone else, and vice versa.
For example, if you do a spell to get a job... You need to make sure you aren't screwing with someone's free will (meaning you shouldn't do a spell to get a specific job and add anything in that might interfere with the decision of whoever will be hiring you). Doing a spell for a specific job might land you the job, but at what cost? What if you forced the person hiring to do so, or caused someone to get fired so that you could get that job? In situations like that, go ahead and try to get the job you really want, but add in something like, "Or it's equivalent or better," (I got that phrase from Marion Weinstein, but I used something similar before), and make sure to add something like, "If it harms none," to try to counteract anything that you might have overlooked in your spell that might cause harm.
Very few things, if anything, are blatantly black and white. Most things fall within the gray area. Choose your words carefully, and be aware of exactly what you're working for.