Weasel words are used as an attempt to deceive or draw attention away from something the speaker does not want noticed, they can be used to make an unfounded assertion. They are popular in politics
They take the form of statements in which the meaning has been sucked out of them, an easy way to spot weasel words is when a statement doesn't seem quite finished:
It can involve a vague generalisation: "More and more people are coming to see that..." Which people? How many is that exactly?
It can involve use of the passive voice to omit an agent: "It has been decided that..." Decided by whom?
I have also seen the term "weasel words" used to describe popular euphemisms such as "freedom fighter" and "collateral damage".
The name "Weasel words" supposedly refers not to a weasel's connotations of being slippery and devious, but to their abilty to suck out an egg while maintaining the shell.