On March 25, 1995, Ward Cunningham launched WikiWikiWeb, the first ever "wiki" website. The idea of the site—then radical—was to allow users to add to and edit the site on the fly. By reducing the barriers for contribution and collaboration, maybe the site would take off. It did, though WikiWikiWeb was innately a bit geeky, as it was devoted to programming topics. But half a decade later, Cunningham's idea inspired Wikipedia.
Cunningham got the word "wiki" from the Wiki Wiki Shuttle, a bus system at the Honolulu airport. The word means "fast" or "quick" in Hawaiian. Indeed, the wiki format proved a fast way to get a body of information onto the web. In its original version, users didn't even have to create accounts to contribute—they simply made edits and optionally could type their name into an edit log (though Cunningham encouraged anonymity). By 2014, a prolonged attack by bots made this unfeasible on WikiWikiWeb, so that original wiki is now read-only.
Here's Cunningham talking about his invention in 2011:
Here's a sample quote from the interview above (emphasis added):
A classic thing on computer communication boards at the time was: You would write something and somebody would spot a spelling error, so they would say "You spelled it this and it’s spelled that!" Because the only place you could write is at the bottom, you could add but you couldn’t change. So you write something and you come back and all you find is tedious complaining about what you said. Now on my system [the wiki, when] you write a spelling error, somebody just fixes it. And you come back and you don’t even notice it was there.
But you find this one sentence that somebody added that really gets at something you were trying to say. So the positive stands out and the negative is just erased. The nice thing there is if somebody comes along in the meantime and is reading, who knows less than you, they might find your partial answer valuable. This idea that every thought is kind of a seed and it just grows and grows and grows [has] been used very effectively on Wikipedia.
Appropriately, one of the best histories of the wiki is the "History of wikis" article on Wikipedia.