particles of food left floating around in your drink after you have taken a sip after swallowing your food or while chewing your food.
Originated in the Central American country of Belize as part of the kriol (creole)(broken English) language spoken there.
Kriol dialect as spoken in Belize.
Dan: "Gimme some a yo coke, mi bally"
Tony taking a look at the pint seeing bread crumbs floating around in the coke
Tony: "Buay, i no tink u want drink some a mi wash-back weh di inya"
Dan: "Let me have some of your soda, pal."
Tony: "I don't think you want to drink from my soda with wash-back food particles floating around in here."