Looks like there's some disagreement about the "Irreflectable duoplet" and "Reflectable duoplet" names.
I changed these terms to "non-reflecting duoplet" and "reflecting duoplet", because no one has ever in the history of Life used the above two terms, as far as I know, and I don't see how anyone ever could: "reflectable duoplet" should mean that the duoplet is able to be reflected, but that's not right. An incoming glider is reflectable, but the duoplet is what is reflecting it.
I'm happy to discuss this kind of thing, but not so happy when changes that I've just made get changed back right away, without even any summary comment to explain why. Wiki editing is a collaborative effort, and to collaborate well it's important to communicate with other collaborators. Silently reverting things without an explanation risks starting an edit war, and edit wars are no fun.
I'm going to try taking out the "corner domino" category, which I added recently and probably shouldn't have. Sometimes "diagonal domino" has been used to refer to duoplet sparks, but that seems seriously confusing now that we have the term "duoplet". Two diagonally connected cells are just plain not domino-shaped -- they're definitely not any kind of -omino, so let's only mention that usage as a historical note. Dvgrn (talk) 14:12, 24 February 2019 (UTC)