Tempura powder is a pre-made batter mix, typically a combination of wheat flour, starch (like corn starch or tapioca starch), and leavening agents (like baking powder), designed to create a light, crispy, and flaky coating for deep-fried foods like seafood, meat, and vegetables. It's a convenient alternative to making batter from scratch, as it's formulated to absorb less oil, resulting in a less fatty and more tender crunch that stays crisp longer.