Refers to edible green vegetables, often leafy greens, as a category. Common in market or cooking contexts.
I bought fresh vegetables at the greengrocer.
It's better to eat greens every day.
blueback fish
Used in fishing and market contexts for fish with a bluish back, such as sardines, mackerel, or saury. Not a scientific term.
Blueback fish are often landed at this fishing port.
Compound of 青 (ao, 'blue/green') and 物 (mono, 'thing'). The vegetable sense comes from the green color of leafy vegetables; the fish sense refers to the bluish back of certain fish.