Wikipedia's definition of "webisode" is basically just episodes of webseries. And while it can be used that way, that's not generally how I think of the term. (TV Tropes seems to get it, though.) Sometimes a TV show (or movie) will have bonus "webisodes" you can watch online, which are generally not more than a few minutes in length, so they're also sometimes called "minisodes." (There may also be other names for them, like "mobisodes" that are released via mobile phones instead of or in addition to the web. And some shows may give their webisodes cute terms based on the show's title or some element of the plot.) They may be one-shots, or part of a miniseries. Some are canonical to the series, and some aren't. I've seen several such things, over the years, and in this section, I'll be listing any of them that I can recall. I'm sure some shows I watch may have done webisodes without my being aware of it, some I may have been aware of but chose not to bother watching, and some I may have watched and later totally forgotten about. So if you can think of anything I may have neglected to include here, please let me know.
I usually think of webisodes as... like I said, "bonus" material that ties into some show or movie... which is why I think of webseries that aren't connected to anything else (with the exception of continued series). But I should mention that even if a series of webisodes is connected to some other TV series or movie, I may in rare cases decide to consider an independent webseries. It can be hard to figure all this out, but usually if I do call a series of webisodes a webseries instead of "just" webisodes, it will be because it has attained a certain length (possibly multiple seasons). But... we'll see. I haven't made any final decisions about such things, as yet.
See also TV micro-series