Crunchiness is the feel and sound of food that is firm and makes a noise when you bite it — the quality of being crunchy. People mostly say it with a smile: the crunchiness of an apple, of fried chicken skin, of a fresh salad, is a reason they like that food. It is not a word you need for sad, stale, or soggy things. You will see it on packets and in food writing more than in short everyday talk; many people just say “it’s so crunchy” instead of naming the crunchiness. Food is the home of the word. You can stretch it a little to other noisy textures, but that is less common.