Groceries are the food and household goods you carry home from the supermarket. Buy the groceries, unpack the groceries, a bag of groceries.
The word is always plural in this sense, and it covers the whole shop rather than any one thing. A grocer once dealt in gross — in bulk — which is where the name comes from, so the trade was wholesale before it was retail.
1noungroceriesFood and household goods bought from a shop.
“Can you help me carry the groceries in from the car?”
groceries is shopping.