It's the same as Wulin in chinese, but in korean, it means "martial forest" or something?
Though usually with the chinese novels you hear about JiangHu instead of Wulin most of the time.
Well I read korean manwha before I even read any chinese webnovels so it might not really be that much of common knowledge.
Anyway, why not just make a footnote to explain what Murim is/means? And even if a reader doesn't have preexisting knowledge they'll find out what Murim means as they read the story.