A Japanese citrus fruit of varying sizes, from squat mandarin to fat round lemon, with minimal juice and plenty of seeds. The zest is highly aromatic. Both zest and juice can be added to dressings with Japanese influences, such as ponzu (mix 1 Tbsp yuzu juice and 1 Tbsp rice wine vinegar or any white vinegar with 2 Tbsp light soy sauce and use to dip sashimi or steamed dumplings), and to a lovely dressing for avocado and chicken salad (mix 1 Tbsp yuzu juice with 2 tsp grain mustard, then mix in 4 Tbsp extra virgin olive oil, and salt and pepper to taste).
For desserts and cakes lemon or orange zest can be replaced with yuzu, but be wary, if the fruits are really ripe and pungent they can be overpowering.
If you have a glut, peel strips of the skin off with a potato peeler (and remove any white pith) and store in an airtight bag in the freezer, or dry at room temperature for a day then blitz with sugar in the food processor to make a delicious yuzu sugar.
You can do the same with coarse salt for a seasoning to sprinkle on fish and seafood. Once the zest or peel is removed, juice the yuzu as best you can and then freeze in ice cube trays and use later in a cocktail, dressing or for a cake icing.
The fruit is in short supply in supermarkets in New Zealand but specialty food stores sometimes have them. The juice, which is often salted, is more readily available.
For more on yuzu see Peter Gordon's article here.