Tempura is a Japanese dish of seafood or vegetables that have been battered and deep-fried.
Tempura batter is traditionally mixed in small batches using chopsticks for only a few seconds, leaving lumps in the mixture that, along with the cold batter temperature, result in the unique fluffy and crisp tempura structure when cooked. The batter is often kept cold by adding ice, or by placing the bowl inside a larger bowl with ice in it. Over mixing the batter will result in the activation of wheat gluten, which causes the flour mixture to become soft and dough-like when fried.
Specially formulated tempura flour is available in worldwide supermarkets. This is generally light (low-gluten) flour, and occasionally contains leaveners such as baking powder. Tempura generally does not use breadcrumbs (panko) in the coating.
Thin slices or strips of vegetables or seafood are dipped in the batter, then briefly deep-fried in hot oil. Vegetable oil or canola oil are most common; however, tempura was traditionally cooked using sesame oil. Many specialty shops still use sesame oil or tea seed oil, and it is thought certain compounds in these oils help to produce light, crispier batter.
Resources1. Wikipedia, Tempura
2. Cooking Light, Tempura Tofu and Spring Vegetables