'Wiki' - W-I-K-I. There can't be many people left who haven't heard of Wikipedia. At least not many who have access to the internet. But ask them what a 'wiki' is, and there's a good chance you'll be met with a blank look and a scratch of the head.

But what is Wikipedia? If you've followed this series from the beginning, you'll have already seen some examples of words which are formed by blending two words together. This is another example - OK, I get the '-pedia' part - that's from encyclopedia, right? Yes, but what about the wiki? In fact it's the 'wiki' part which is the USP (unique selling point) of Wikipedia. It means that anyone can contribute their own information and content to the site. It's open to anybody, anywhere at any time.

The 'wiki' part is actually a Hawaiian word meaning 'quickly'. Ward Cunningham, the man credited with developing the wiki concept for the internet, was at Honolulu airport in Hawaii and was told to take the 'wiki wiki bus'. He was understandably confused and when he asked what it meant was told it simply meant the quick bus. He liked it so much he decided to name his new web project after it.

Basically, wikis are websites which are very easy to set up, because they generally use WYSIWYG tools (see Series 2) and they can then be edited by anybody - you don't have to be the creator of the site to add more content. They are used in education, for class projects, in business and even in politics.

But the open nature of wikis and their ease of use can be a disadvantage. In 2006 the UK government department for environment, food and rural affairs (DEFRA) set up a wiki to invite discussion about new environmental policies. Unfortunately, not all the contributions were entirely serious. In reply to the question, 'What tools can be used to deliver the environmental contract?' one contributor wrote: 'Spade, Organic Yoghurt Stirrer, Old washing up liquid bottle, Sticky Back Plastic'.

At the time some reports of the story were along the lines of 'Hackers deface government website', a headline which totally missed the point that the key to wikis is the fact that they are open and can be added to by anybody and that's exactly what happened in this case. The UK government might think twice before setting up another wiki.