probably a drop of relief.
The curve of your neck has to match the curve the vibrating string makes.
to flat: buzzing at the first five strings
to much curve: buzzing above the 12th fret
just right: buzzing everywhere
But mind you: this is all within a normal action range and with a proper neck. If the action is already unusually high something else is going on.
Also: I presume the buzzing is not only there with an open string. If that's the case your nut can be cut out to low.