No no, "fandiscs" are officially released products, so called because they're for the fans, and/or "fanservicy". They're usually released after the main product, assuming it did well in sales. Sometimes they're canon, sometimes they're not.
"Fan-made" visual novels are unofficial, made by fans, and don't really have any other specific name by which they're called. Well that's not entirely true, the word "doujinshi" is a blanket term for those kinds of things (at least in Japan). They're obviously not canon.