Aggregate is the granular filler in concrete and the base material under slabs, pavers and driveways. In concrete it is split into fine aggregate (sand, particles smaller than about 3/16”) and coarse aggregate (gravel or crushed stone, typically 3/8”–1”). Together they make up roughly 60–75% of a concrete mix by volume; the portland cement paste just glues them together. In the US, concrete aggregates are graded under ASTM C33, and residential ready-mix usually uses a maximum coarse size of 3/4” — small enough to flow around rebar in a 4” slab.
Outside the mix, aggregate is sold by number grade. #57 stone (about 3/4”–1”, no fines) drains well and is the standard driveway top layer and drainage rock. Crusher run (also called dense grade, DGA or ¾” minus) contains fines that lock together when compacted, which makes it the go-to base under slabs and pavers. Pea gravel is small and rounded — nice underfoot, but it never locks, so it makes a poor base.
Bulk aggregate is sold by the ton at quarries and by the cubic yard at landscape yards. Crushed stone weighs about 1.4 tons per yd³ (2,800 lbs), so 10 tons is roughly 7 yd³ — always confirm which unit a quote uses before comparing prices.