Because it's "ampersand." It's just pointing out your mental deficiency for misspelling it twice in a row.
A URL has any number of arguments, and the order doesn't matter. That is, your original had "v=..." and "feature=..." (or something like that). These arguments are separated by '&', and the '?' separates the web address from the list of arguments. That is, URLs are like
Code:
http://some.server/some_page?argument_1=something&argument_2=something&...
In the case of our youtube embedder, it can only have a single argument, the "v=..." part. Everything else, regardless of ordering in the original url, must be removed.