Spread thin. If something is sparse, there is not much of it, and what there is sits far apart with gaps in between. That second half matters — 'sparse' is not simply 'a small amount', it is a small amount spread over a wide space. Sparse hair means you can see scalp between the hairs. A sparse crowd means people standing here and there in a big room, not a small tight group. Sparse trees means a few trees with a lot of empty ground between them. So the word always carries a picture of area, and of emptiness showing through. It is used for things you could count or see spread out: hair, trees, population, traffic, notes, furniture, applause. It is also common with information — 'the details are sparse', meaning we were told very little and there are holes in what we know. The word feels a bit formal or written. In casual speech people are more likely to say 'there weren't many people' than 'the crowd was sparse'. You will meet it most in news writing, reports, and academic English.