Merriam-Webster defines concern as "a matter that causes feelings of unease, uncertainty, or apprehension."
The definition holds as true in the NFL as it does anywhere else.
For some teams, those concerns are glaring. It could be an uncertain or dire situation at quarterback. A leaky offensive line. A porous defense. Or a roster and/or organization that is seemingly in shambles from top to bottom.
It's usually not difficult to see why bottom-feeders are bottom-feeders.
However, for the league's better teams, concerns can be trickier to spot. Maybe it's a weakness at one position that threatens to derail a deep postseason run.