A wiki is a web site designed to be extremely easy to edit.

The original wiki is at Nowadays there are many more wikis. Wikipedia is only one example of a wiki, and not a very typical one, but it's much better known than the others, so some people think "wiki" is short for "Wikipedia", which is annoying ... I'll all in favour of neologisms, but not when they try to overwrite really useful preexisting words!

See for more definitions.

See for Ward Cunningham's original ideas about what a wiki should be like. bolzano breaks the openness principle by requiring a password for editing (because without the immense user base of Wikipedia it's hard to deal with spam) but follows all the other principles.