Guindilla peppers are mild, tangy, yellowish-green chili peppers from Spain's Basque region, famous when pickled in white wine vinegar as piparras, offering a slight heat and sweet-tart flavor, perfect for tapas (like Gildas with anchovies), alongside cheeses, in Bloody Marys, or as a snack. They're narrow, elongated, and have a crisp bite, providing a flavorful addition to Spanish cuisine.