A form of divination, originating on the Counterweight Continent, which involves casting yarrow stalks and methodically counting how many fall in a particular orientation, then looking up the correct oracular verse out of eight thousand, eight hundred and eighty-eight. (Yes: it's that number again. A simpler version, though frowned upon by purists and impractical in Ankh-Morpork where it's difficult (if not impossible) to get the money back afterwards, involves throwing three coins eight times. (hence the name).
One result, mentioned in Mort, is the octogrammatic oracular verse 8,887 Illegibility: or The Atoning Goose. This left the superior person consulting the ChingAling very much none the wiser.
To Roundworld, China, and the I Ching.