Meat puppets
The term meat puppet is a term used most notably on Wikipedia as an off shoot of their term sock puppet, which basically means someone with 2 or more accounts - the 2nd or additional accounts are referred to as sock puppets. A meat puppet, however, is actually a different person, but one who is told to act in coordination with the others.
For example:
John is trying to edit an article about Australia to try to suggest that its political system really does resemble communism. A variety of other people on Wikipedia disagree and suggest that a socialist democracy or alternatively a constitutional democracy are more apt descriptions. John is outnumbered 20:1.
John then calls some friends of his from all over the country and also overseas, people who are not using the same ISP as he is. He asks them to please support him. John asks his friends to please write in there why the Australian political system resembles communism. John might even instruct his friends as to what to say, pointing to a page of evidence that says why Australia's political system really does resemble communism.
John's friends cannot be banned as sock puppets - clearly they are all different people. They live in different parts of the country, even different parts of the world, with different ISPs, they login all at the same time, and so forth. But they can still be breaking the rules by acting as one person.
Wikipedia of course is not a democracy, and, at least in theory, how many people support one idea shouldn't actually matter, as it should be the strength of the argument and the facts of the argument that matters more than its popularity. The problem is that in reality there has to be some way to measure whether something is true or not, and one of the major ways that this is done is through counting.
The meat puppetry rule is applied inconsistently.
For example Janeyryan, who is obviously speaking in a way that is meant to convince people that he is Chip Berlet is not being penalised because they cannot prove 100% that they are a sock puppet account. They can prove that they are abusive, that they are controlling articles and that they are doing a number of things which to any normal person would get them banned, and that they are not a new user - but due to some technicality they are not being banned, because in theory they might simply be a meat puppet.
A number of banned users have asked friends to log on to Wikipedia to speak for them. In numerous such occasions, these friends were banned for doing so, for continuing to edit in the same way.
In cases where 2 accounts seem to be the same person, but you cannot prove 100% that they are, they generally get called meat puppets. It is perhaps a slightly lesser crime, although in many cases it turns out that they were the same person anyway.