What does Dickinson mean when she says zero at the bone?

The speaker of Dickinson's poem "Because I could not stop for Death--" refers to zero at the bone metaphorically representing the moment of death, when physical sensations cease and the body becomes still and cold.

In the context of the poem, where Death takes the speaker on a carriage ride representing her journey towards dying, reaching "Zero at the bone" symbolizes the complete absence of life and vitality within her at the moment of transition to the afterlife.