What is Crab apple?

The small, sour fruit of the wild apple tree. Crab apples are generally too tart to eat raw and are more commonly used to make a sweet jelly for scones and brioches, or as a condiment for roasted meats and game. They're also used to make crab apple wine. As they're not grown commercially they're not readily available to buy. You're more likely to find them at farmers' markets or farm shops and pick-your-own farms.