What is parsing?

[SturmChurro]

Unless they are purposely afking all simultaneously...How would you know that? You must use an addon to know they aren't doing well, no? 8) dumdum duum

No. It's quite easy to tell when player(s) are underperforming with a quick glance at information available in-game. What is this thread anyway?

[Naaura]

No. It's quite easy to tell when player(s) are underperforming with a quick glance at information available in-game. What is this thread anyway?

I would like to know how one can tell if others are underperforming if you can tell how. I personally cant tell unless I can visually see that they are distracted and just not doing their rotation and following boss mechanics.
And this thread is about what is parsing because I kept hearing for years but I finally remembered to ask since it was mentioned earlier