Weasel Words are about words or phrases that imply more than they actually mean. Taken at face value, they don't say much at all, or are just not impressive. However, the way they're used imply there's substance to them, that they mean something.
This is one reason they're a common feature of advertising, both on television and elsewhere: companies can imply that products or offers are better than they actually are without getting into legal trouble for lying about it. For instance, "part of this complete breakfast" doesn't mean the product itself completes the breakfast, but the implication is that it does.
For an extensive and detailed examination of Weasel Words, see this entry at Wikipedia. Or, better yet, see this entry! Some people say that weasel words are a necessary generalisation. TV Tropes editor Sockatume believes that if you know who's saying something, you should mention it.
Do you see what we did there?
For one form of weasel words we don't want around here, see Examples Are Not Arguable. As an interesting note the term is called that not to imply weasels are inherently evil somehow, but rather in reference to how they eat eggs by sucking the insides out and only make a small hole, meaning an egg they have sucked may appear to be intact until someone looks at it more closely, in the same way weasel words suck the meaning out of a statement without being immediately obvious.
- Adjacent to This Complete Breakfast: Like the description says, this is trying to imply that the product is what completes the breakfast, but in actuality, it's only adjacent to it.
- All-Natural Snake Oil: Using the word 'natural' or similar to describe a product in advertising. This is weasel wording because sometimes Nature Is Not Nice, and sometimes only part of the product is natural.
- Asbestos-Free Cereal: Implying that a food product is good for you because it lacks something that's obviously bad, while saying nothing about what it does contain, which may be more important information.
- Absolute Comparative: Advertising a product by using a comparison that sounds positive but doesn't really mean anything (for example, a pillow being described as "30% softer" than most pillows is an example of this because softness isn't really something you can measure).
- Best is Average, Better is Best: Everyone's claiming their product is "the best", but that means that "best" is now "normal", so they need permission to claim it's better.
- Crunchtastic: Describing a product with made-up words that sound positive because they end in the endings of positive words, such as "(l)icious", "(r)ific", or "tastic", but because these words are made-up, they don't mean anything.
- Damned by Faint Praise: Praising something you don't actually like by pointing out something that may be true but is so mundane/weak/beside the point that pointing it out isn't really a compliment.
- Just Pennies a Day: Making something expensive seem cheap by splitting the full price into "X dollars/pounds/whatever per [relatively short period of time]".
- Lite Crème: Misspelling a word when the ingredient it suggests isn't there or is hardly there. It's weasel wording because, for example, "creme" implies there is cream, when there actually isn't.
- Never Needs Sharpening: Making the product seem positive by saying that it "doesn't need X", when in reality, it breaks when you do X with it.
- New and Improved: A product is changed slightly and so advertisers hype up the fact that it's "new". The implication is that new = good, but it's not necessarily the case.
- People's Republic of Tyranny: Naming an oppressive republic something that points out the fact that it's democratic to try and make it sound not-oppressive.
- Quote Mine: Taking a quote from something to prove a point, but the context gives the quote a different meaning.
- Up to __ or More: Using the phrase "up to X or more" to advertise something, which is meaningless because "up to X or more" could be anything.
- It has been said that browsing TV Tropes will help you win the lottery. But honestly, you're better off investing in a good company.