Ak'voh was an ancient Klingon tradition wherein, after a warrior had died in battle, his comrades stayed with the body to keep away predators, an act which allowed the spirit to leave the body when it was ready for the long journey to Sto-vo-kor.
The idea of Klingons keeping vigil over the bodies of the dead seems at odds with the Klingon death ritual, wherein a corpse was considered a worthless shell immediately upon death. Since Worf calls the ak'voh an ancient tradition, perhaps it is no longer commonly practiced, but Worf was familiar with it due to his studies of ancient Klingon culture. It may reflect an earlier conception of the journey to Sto-vo-kor. Star Trek: Discovery depictions of Klingons showed their reverence for the dead body.
Alternately, it may have been something Worf made up entirely to make amends with O'Brien, as he did when inventing the gik'tal to test Sito Jaxa.