A punnet is a small light basket or other container for fruit or vegetables. The weight varies from country to country.
Originally, they were a round woodchip basket but nowadays, they are square to rectangular and made of plastic. They can also be made of more sustainable materials like moulded pulp or corrugated cardboard.
A punnet of fresh blueberries, 170g (6oz). They are also sold in 450g (1Ib) containers.