They could explain the term. But the person I replied to specifically said MMOs were about
all about grinding. First of all, he used the incorrect terminology since MMOs aren't about grinding they're about a 24/7 online multiplayer world (they're not even necessarily MMORPGs either
I find it unfortunate you don't understand the psychology behind grinding. Perhaps I'll be able to explain it to you further down the line.
Now that we covered MMOs lets talk about RPGs.
RPGs were never necessarily about grinding either (which again, leaves room for grinding being an essential part of an RPG but the ones I mentioned didn't contain it which proves without a shed of a doubt grind isn't a necessary component of the RPG genre). None of the examples I gave are. But you know what all RPGs have in common? They don't have PvP.
Grinding gear in PvP game for linear progression is rare.
"The grind" is optional in games, including in MMORPG. If you compare WoW to say CoD then the progression in CoD multiplayer is leveling from XP as well as several other metagames. But the progression path ("grind") isn't linear.
Unlike WoW, you have a very good chance to kill enemies with the default builds provided you are skilled in FPS.
Now, we are to believe that suddenly the combination of MMO and RPG requires grinds as if some kind of macabre combination of the two suddenly invented the anti christ. This is patently false. To understand this we must first understand the term grind is relative, and that WoW is the creme de la creme of grinding. Second, we must look what an RPG is
at its core about
: developing the character with storyline, leveling/experience (which unlocks the former), and gear (which unlocks the former).
In PvP WoW, unlike in RPGs, more gear doesn't unlock content. Now, there are 3 ways to
end an RPG: 1) it becomes more and more difficult (nearly impossible?) the more you reach the end level. Hello Nethack. 2) you accept the game ends at end game and call the game. Original GW2. 3) you make either the leveling or the "end-game" (= max level) incredibly grindy (time spend on tedious). WoW what a revelation.