means The act of leaving someone or splitting something into separate pieces — whether a farewell, a separation, or the line where combed hair divides.

from From Old English 'dǣlan' lurking behind the verb 'part,' but the word itself comes through 'part' from Latin 'pars, partis' — a portion, a share. The '-ing' simply turns the splitting into an event. So a 'parting' is literally a making-into-parts: of a crowd, of hair, of two people who used to be one 'we.'