Sparsity is the condition of not having enough of something. You might notice the sparsity of hair on your grandpa's head — but if you're polite, you won't bring it up.
You can talk about the sparsity of grass in your brown and patchy lawn, or the sparsity of customers at your mac-and-cheese food truck. Whenever there's a shortage, a lack, or a deficiency of something, it's in a state of sparsity. Sparsity comes from the Latin sparsus, the past participle of a verb meaning "to strew or scatter."