Nibby is an informal term for cocoa nibs: the dried, fermented, and roasted pieces of cracked cocoa beans, used as a crunchy, intensely chocolate ingredient before they're ground into cocoa powder or conditioned into chocolate.
Cocoa nibs have a bittersweet, concentrated chocolate flavor and a texture similar to coarsely chopped nuts. They're commonly sprinkled over ice cream, yogurt, oatmeal, and baked goods, or mixed into granola, and pair well with fruit, nuts, coffee, and even savory dishes like meat rubs, where their bitterness balances rich or fatty flavors. Craft chocolate makers also use nibs to showcase the character of a single bean origin before it's fully processed into a bar.
Because nibs are unsweetened and quite bitter on their own, recipes that add them need enough sugar, salt, or fat elsewhere in the dish to balance them.