Headphones

I've heard it being used in several reviews and comments, most notably it's column being removed from Crinacle's database. I know it might generally deal with lower mids and higher bass, though I have no idea what it definitively is. I tried to find out what it is, but I couldn't find any info other than mentions of it on several subreddits as well as Google. So what is note weight definitively, and why did Crinacle have a column for it in the first place, then neglect it and ultimately remove it?