Concrete
A building material made by mixing cement, water, sand, and stone. The cement and water react chemically to bind the sand and stone into an artificial rock.
What does concrete mean?
Concrete is not a single product but a recipe, and the proportions of that recipe determine everything about how it performs. The cement paste is the expensive, reactive part; the sand and stone are the cheap, stable filler that gives the material its bulk and stability. Because the binding action is a chemical reaction rather than drying, concrete hardens underwater and keeps gaining strength for months.
In practice
Every conversation about a driveway, slab, or footing is really a conversation about which concrete recipe is being delivered, which is why suppliers ask for a strength and a slump rather than just a quantity.