(n.) a churchyard path
A bierbalk is a churchyard path—and in particular, a path connecting the gate of the churchyard to the church itself.
That’s a definition from the first volume of the English Dialect Dictionary published in 1898. But this word has been recorded as far back as the sixteenth century, and its etymological roots are even more ancient than that.
Bier is an Old English word for some kind of handled framework for carrying or bearing something—like the poles of a stretcher, or the handles of a wheelbarrow. But it was also used of the moveable framework on which a coffin was laid before burial, or carried through a churchyard to the church or grave.
A balk, meanwhile, was originally a raised ridge of land, or one of the elongated piles of earth left by a plough; to make a balk, proverbially, is to leave an area of land accidentally unploughed. By extension, balk also came to be used not only of the pile of earth that covered a grave, but also of a long raised pathway or walkway running alongside (or over the top of) a ridge of land.
Whichever of these two meanings is meant to be implied in this word is unclear, but put together a bierbalk is the path that leads from the lichgate of a churchyard to the church building itself—namely, the very last path a coffin would be carried along before being interred.