Outside of the discussion that spawned this post I havent ever heard of the distinction between melodeath and melodic death metal. Not online and not IRL. Not saying some use it but it sure isnt widespread. For me its the same thing though - I never saw a distinction. There is obviously bands that lean more on the melodic and heavy metal side and bands that lean more on the death metal side of things.
Im guessing you are scandinavian by the username that you use. In swedish I use the terms in the same way, to mean the same thing - "melodöds", "melodisk döds" and "melodisk dödsmetall".
Why does it seem like you always have amnesia? We've discussed my user name before.
Also, maybe you haven't been on this forum long enough to have experienced the various discussions that distinguish between Melodic Death Metal (death metal with pronounced melodic tendencies) and 'Melodeath' (a partially pejorative term to describe 'extreme heavy/power metal' and thus differentiate it from death metal). However, the discussion has been repeated ad nauseum. Here's proof:
Search history.
As I've already said, it's used very informally, and for the purposes of distinguishing two clearly distinct style of metal from one another, in the same manner that the term 'flower metal' is used. Because it's silly to say that
With Fear I Kiss the Burning Darkness and
Follow the Reaper are part of the same sub-genre. It's nonsensical use the term 'melodic death metal' to refer to a style of music that has nothing in common musically with death metal. 'Gothenburg' doesn't work because the term applies equally to the traditional Swedish death metal vein, so 'melodeath' was at some point appropriated to maintain the familiarity of the term while providing the necessary distinction.
As far as whether or not it's widespread, 'widespread' in this case is obviously relative. It is used on every metal forum that I've posted on that actually discusses extreme metal, including the Nuclear War Now! forum, Metal Rules, and Metal Archives, so it obviously extends beyond a couple of people on Ultimate Metal. But regardless of that, the post that LuminousAether was referencing should be taken in the context of the lexicon of the forum anyway, which, in this case, already has a (disputed) propensity to use the phrase in the manner I've previously described.
Now, before I am accused of taking things too seriously, I will rephrase and summarize my original point thusly:
In discussions wherein it becomes necessary or beneficial to introduce a distinction between the two forms of metal often associated with the term 'melodic death metal', in order to avoid confusion, the style that is derived from heavy/power metal may be referred to as 'melodeath' for convenience.